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 $59.97   6.795%   $64.045   $64.05   $64.05   $64.00  
  Purchase #2 $176.71   10.573%   $195.3935   $195.39   $195.40   $195.40  
  Purchase #3 $115.79   8.727%   $125.895   $125.90   $125.90   $125.90  
  Purchase #4 $56.59   7.793%   $61.0001   $61.00   $61.00   $61.00  
  Purchase #5 $115.99   7.195%   $124.3355   $124.34   $124.35   $124.30  
  Purchase #6 $132.59   13.130%   $149.9991   $150.00   $150.00   $150.00  
  Purchase #7 $140.87   6.686%   $150.2886   $150.29   $150.30   $150.30  
  7 purchase totals = $798.51       $870.9568   $870.97   $871.00   $870.90