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 $117.82   6.263%   $125.1991   $125.20   $125.20   $125.20  
  Purchase #2 $202.78   4.261%   $211.4205   $211.42   $211.40   $211.40  
  Purchase #3 $144.53   11.834%   $161.6337   $161.63   $161.65   $161.60  
  Purchase #4 $60.36   13.436%   $68.47   $68.47   $68.45   $68.50  
  Purchase #5 $224.50   11.159%   $249.552   $249.55   $249.55   $249.60  
  Purchase #6 $126.69   11.705%   $141.5191   $141.52   $141.50   $141.50  
  Purchase #7 $41.89   11.655%   $46.7723   $46.77   $46.75   $46.80  
  7 purchase totals = $918.57       $1,004.5667   $1,004.56   $1,004.50   $1,004.60