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 $166.73   11.558%   $186.0007   $186.00   $186.00   $186.00  
  Purchase #2 $141.59   4.295%   $147.6713   $147.67   $147.65   $147.70  
  Purchase #3 $218.34   4.786%   $228.7898   $228.79   $228.80   $228.80  
  Purchase #4 $194.53   10.839%   $215.6151   $215.62   $215.60   $215.60  
  Purchase #5 $40.90   13.114%   $46.2636   $46.26   $46.25   $46.30  
  Purchase #6 $199.98   8.755%   $217.4882   $217.49   $217.50   $217.50  
  Purchase #7 $238.99   6.477%   $254.4694   $254.47   $254.45   $254.50  
  7 purchase totals = $1,201.06       $1,296.2981   $1,296.30   $1,296.25   $1,296.40