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 $125.46   12.751%   $141.4574   $141.46   $141.45   $141.50  
  Purchase #2 $236.46   8.306%   $256.1004   $256.10   $256.10   $256.10  
  Purchase #3 $99.79   4.654%   $104.4342   $104.43   $104.45   $104.40  
  Purchase #4 $50.33   8.807%   $54.7626   $54.76   $54.75   $54.80  
  Purchase #5 $108.56   10.339%   $119.784   $119.78   $119.80   $119.80  
  Purchase #6 $203.53   4.131%   $211.9378   $211.94   $211.95   $211.90  
  Purchase #7 $98.82   7.482%   $106.2137   $106.21   $106.20   $106.20  
  7 purchase totals = $922.95       $994.6901   $994.68   $994.70   $994.70