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 $119.71   12.532%   $134.7121   $134.71   $134.70   $134.70  
  Purchase #2 $168.48   7.163%   $180.5482   $180.55   $180.55   $180.50  
  Purchase #3 $194.47   7.499%   $209.0533   $209.05   $209.05   $209.10  
  Purchase #4 $249.41   13.133%   $282.165   $282.17   $282.15   $282.20  
  Purchase #5 $61.30   11.802%   $68.5346   $68.53   $68.55   $68.50  
  Purchase #6 $44.64   9.571%   $48.9125   $48.91   $48.90   $48.90  
  Purchase #7 $88.30   3.716%   $91.5812   $91.58   $91.60   $91.60  
  7 purchase totals = $926.31       $1,015.5069   $1,015.50   $1,015.50   $1,015.50