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 $53.81   8.731%   $58.5082   $58.51   $58.50   $58.50  
  Purchase #2 $66.25   9.431%   $72.498   $72.50   $72.50   $72.50  
  Purchase #3 $67.94   12.312%   $76.3048   $76.30   $76.30   $76.30  
  Purchase #4 $110.59   13.455%   $125.4699   $125.47   $125.45   $125.50  
  Purchase #5 $183.94   11.610%   $205.2954   $205.30   $205.30   $205.30  
  Purchase #6 $199.52   7.239%   $213.9633   $213.96   $213.95   $214.00  
  Purchase #7 $199.27   12.482%   $224.1429   $224.14   $224.15   $224.10  
  7 purchase totals = $881.32       $976.1825   $976.18   $976.15   $976.20