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 $118.46   11.724%   $132.3483   $132.35   $132.35   $132.30  
  Purchase #2 $43.74   10.130%   $48.1709   $48.17   $48.15   $48.20  
  Purchase #3 $102.34   10.174%   $112.7521   $112.75   $112.75   $112.80  
  Purchase #4 $184.91   5.222%   $194.566   $194.57   $194.55   $194.60  
  Purchase #5 $86.71   4.223%   $90.3718   $90.37   $90.35   $90.40  
  Purchase #6 $225.58   12.596%   $253.9941   $253.99   $254.00   $254.00  
  Purchase #7 $72.77   4.409%   $75.9784   $75.98   $76.00   $76.00  
  7 purchase totals = $834.51       $908.1816   $908.18   $908.15   $908.30