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 $88.55   8.330%   $95.9262   $95.93   $95.95   $95.90  
  Purchase #2 $250.39   4.212%   $260.9364   $260.94   $260.95   $260.90  
  Purchase #3 $61.43   11.583%   $68.5454   $68.55   $68.55   $68.50  
  Purchase #4 $21.75   5.485%   $22.943   $22.94   $22.95   $22.90  
  Purchase #5 $94.54   5.223%   $99.4778   $99.48   $99.50   $99.50  
  Purchase #6 $227.92   9.385%   $249.3103   $249.31   $249.30   $249.30  
  Purchase #7 $128.50   4.533%   $134.3249   $134.32   $134.30   $134.30  
  7 purchase totals = $873.08       $931.4640   $931.47   $931.50   $931.30