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 $54.92   8.419%   $59.5437   $59.54   $59.55   $59.50  
  Purchase #2 $73.32   12.111%   $82.1998   $82.20   $82.20   $82.20  
  Purchase #3 $163.60   4.793%   $171.4413   $171.44   $171.45   $171.40  
  Purchase #4 $101.72   13.344%   $115.2935   $115.29   $115.30   $115.30  
  Purchase #5 $234.37   8.287%   $253.7922   $253.79   $253.80   $253.80  
  Purchase #6 $217.92   12.257%   $244.6305   $244.63   $244.65   $244.60  
  Purchase #7 $129.46   4.628%   $135.4514   $135.45   $135.45   $135.50  
  7 purchase totals = $975.31       $1,062.3524   $1,062.34   $1,062.40   $1,062.30