Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.61   13.733%   $207.6878   $207.69   $207.70   $207.70  
  Purchase #2 $174.32   7.289%   $187.0262   $187.03   $187.05   $187.00  
  Purchase #3 $210.53   8.869%   $229.2019   $229.20   $229.20   $229.20  
  Purchase #4 $156.72   10.537%   $173.2336   $173.23   $173.25   $173.20  
  Purchase #5 $119.99   3.126%   $123.7409   $123.74   $123.75   $123.70  
  Purchase #6 $122.83   9.480%   $134.4743   $134.47   $134.45   $134.50  
  Purchase #7 $216.61   13.572%   $246.0083   $246.01   $246.00   $246.00  
  7 purchase totals = $1,183.61       $1,301.3730   $1,301.37   $1,301.40   $1,301.30