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 $91.45   6.781%   $97.6512   $97.65   $97.65   $97.70  
  Purchase #2 $98.97   13.126%   $111.9608   $111.96   $111.95   $112.00  
  Purchase #3 $59.43   11.629%   $66.3411   $66.34   $66.35   $66.30  
  Purchase #4 $44.89   10.561%   $49.6308   $49.63   $49.65   $49.60  
  Purchase #5 $78.56   13.235%   $88.9574   $88.96   $88.95   $89.00  
  Purchase #6 $124.26   6.396%   $132.2077   $132.21   $132.20   $132.20  
  Purchase #7 $210.88   10.697%   $233.4378   $233.44   $233.45   $233.40  
  7 purchase totals = $708.44       $780.1868   $780.19   $780.20   $780.20