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 $41.71   11.119%   $46.3477   $46.35   $46.35   $46.30  
  Purchase #2 $169.39   6.402%   $180.2343   $180.23   $180.25   $180.20  
  Purchase #3 $20.40   11.412%   $22.728   $22.73   $22.75   $22.70  
  Purchase #4 $64.43   10.816%   $71.3987   $71.40   $71.40   $71.40  
  Purchase #5 $75.67   11.476%   $84.3539   $84.35   $84.35   $84.40  
  Purchase #6 $26.56   9.642%   $29.1209   $29.12   $29.10   $29.10  
  Purchase #7 $154.58   9.278%   $168.9219   $168.92   $168.90   $168.90  
  7 purchase totals = $552.74       $603.1054   $603.10   $603.10   $603.00