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 $166.87   8.832%   $181.608   $181.61   $181.60   $181.60  
  Purchase #2 $126.56   13.413%   $143.5355   $143.54   $143.55   $143.50  
  Purchase #3 $223.74   6.787%   $238.9252   $238.93   $238.95   $238.90  
  Purchase #4 $77.75   13.593%   $88.3186   $88.32   $88.30   $88.30  
  Purchase #5 $250.82   4.228%   $261.4247   $261.42   $261.40   $261.40  
  Purchase #6 $44.74   9.423%   $48.9559   $48.96   $48.95   $49.00  
  Purchase #7 $169.28   10.308%   $186.7294   $186.73   $186.75   $186.70  
  7 purchase totals = $1,059.76       $1,149.4973   $1,149.51   $1,149.50   $1,149.40