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 $92.34   6.761%   $98.5831   $98.58   $98.60   $98.60  
  Purchase #2 $141.52   11.411%   $157.6688   $157.67   $157.65   $157.70  
  Purchase #3 $123.42   8.317%   $133.6848   $133.68   $133.70   $133.70  
  Purchase #4 $53.92   12.152%   $60.4724   $60.47   $60.45   $60.50  
  Purchase #5 $199.48   4.821%   $209.0969   $209.10   $209.10   $209.10  
  Purchase #6 $140.33   12.698%   $158.1491   $158.15   $158.15   $158.10  
  Purchase #7 $169.47   9.584%   $185.712   $185.71   $185.70   $185.70  
  7 purchase totals = $920.48       $1,003.3671   $1,003.36   $1,003.35   $1,003.40