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 $81.40   8.487%   $88.3084   $88.31   $88.30   $88.30  
  Purchase #2 $30.81   7.262%   $33.0474   $33.05   $33.05   $33.00  
  Purchase #3 $112.34   7.288%   $120.5273   $120.53   $120.55   $120.50  
  Purchase #4 $72.45   4.193%   $75.4878   $75.49   $75.50   $75.50  
  Purchase #5 $55.40   13.837%   $63.0657   $63.07   $63.05   $63.10  
  Purchase #6 $65.95   9.382%   $72.1374   $72.14   $72.15   $72.10  
  Purchase #7 $10.95   11.151%   $12.171   $12.17   $12.15   $12.20  
  7 purchase totals = $429.30       $464.7450   $464.76   $464.75   $464.70