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 $66.41   3.413%   $68.6766   $68.68   $68.70   $68.70  
  Purchase #2 $149.28   3.192%   $154.045   $154.05   $154.05   $154.00  
  Purchase #3 $59.59   10.665%   $65.9453   $65.95   $65.95   $65.90  
  Purchase #4 $113.28   5.163%   $119.1286   $119.13   $119.15   $119.10  
  Purchase #5 $75.89   5.312%   $79.9213   $79.92   $79.90   $79.90  
  Purchase #6 $205.98   4.644%   $215.5457   $215.55   $215.55   $215.50  
  Purchase #7 $55.98   6.191%   $59.4457   $59.45   $59.45   $59.40  
  7 purchase totals = $726.41       $762.7082   $762.73   $762.75   $762.50