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 $172.59   12.556%   $194.2604   $194.26   $194.25   $194.30  
  Purchase #2 $76.64   3.807%   $79.5577   $79.56   $79.55   $79.60  
  Purchase #3 $190.27   4.452%   $198.7408   $198.74   $198.75   $198.70  
  Purchase #4 $27.35   8.230%   $29.6009   $29.60   $29.60   $29.60  
  Purchase #5 $189.27   4.584%   $197.9461   $197.95   $197.95   $197.90  
  Purchase #6 $86.87   5.335%   $91.5045   $91.50   $91.50   $91.50  
  Purchase #7 $151.95   5.520%   $160.3376   $160.34   $160.35   $160.30  
  7 purchase totals = $894.94       $951.9480   $951.95   $951.95   $951.90