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 $183.76   7.588%   $197.7037   $197.70   $197.70   $197.70  
  Purchase #2 $171.89   7.439%   $184.6769   $184.68   $184.70   $184.70  
  Purchase #3 $64.76   6.227%   $68.7926   $68.79   $68.80   $68.80  
  Purchase #4 $120.91   8.325%   $130.9758   $130.98   $131.00   $131.00  
  Purchase #5 $249.90   9.507%   $273.658   $273.66   $273.65   $273.70  
  Purchase #6 $223.50   10.754%   $247.5352   $247.54   $247.55   $247.50  
  Purchase #7 $123.57   13.205%   $139.8874   $139.89   $139.90   $139.90  
  7 purchase totals = $1,138.29       $1,243.2296   $1,243.24   $1,243.30   $1,243.30