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 $243.28   10.711%   $269.3377   $269.34   $269.35   $269.30  
  Purchase #2 $48.43   3.630%   $50.188   $50.19   $50.20   $50.20  
  Purchase #3 $57.93   13.483%   $65.7407   $65.74   $65.75   $65.70  
  Purchase #4 $84.30   8.739%   $91.667   $91.67   $91.65   $91.70  
  Purchase #5 $59.57   8.660%   $64.7288   $64.73   $64.75   $64.70  
  Purchase #6 $183.96   8.260%   $199.1551   $199.16   $199.15   $199.20  
  Purchase #7 $11.42   10.584%   $12.6287   $12.63   $12.65   $12.60  
  7 purchase totals = $688.89       $753.4460   $753.46   $753.50   $753.40