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 $66.52   11.491%   $74.1638   $74.16   $74.15   $74.20  
  Purchase #2 $154.66   9.235%   $168.9429   $168.94   $168.95   $168.90  
  Purchase #3 $93.50   10.530%   $103.3456   $103.35   $103.35   $103.30  
  Purchase #4 $95.67   12.579%   $107.7043   $107.70   $107.70   $107.70  
  Purchase #5 $164.33   11.240%   $182.8007   $182.80   $182.80   $182.80  
  Purchase #6 $7.83   4.695%   $8.1976   $8.20   $8.20   $8.20  
  Purchase #7 $240.75   4.408%   $251.3623   $251.36   $251.35   $251.40  
  7 purchase totals = $823.26       $896.5172   $896.51   $896.50   $896.50