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 $59.34   6.107%   $62.9639   $62.96   $62.95   $63.00  
  Purchase #2 $81.97   5.733%   $86.6693   $86.67   $86.65   $86.70  
  Purchase #3 $113.65   11.824%   $127.088   $127.09   $127.10   $127.10  
  Purchase #4 $237.48   10.681%   $262.8452   $262.85   $262.85   $262.80  
  Purchase #5 $41.36   4.468%   $43.208   $43.21   $43.20   $43.20  
  Purchase #6 $41.92   10.191%   $46.1921   $46.19   $46.20   $46.20  
  Purchase #7 $135.58   4.693%   $141.9428   $141.94   $141.95   $141.90  
  7 purchase totals = $711.30       $770.9093   $770.91   $770.90   $770.90