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 $59.39   9.802%   $65.2114   $65.21   $65.20   $65.20  
  Purchase #2 $193.27   6.659%   $206.1398   $206.14   $206.15   $206.10  
  Purchase #3 $62.63   3.764%   $64.9874   $64.99   $65.00   $65.00  
  Purchase #4 $117.33   10.782%   $129.9805   $129.98   $130.00   $130.00  
  Purchase #5 $36.29   6.197%   $38.5389   $38.54   $38.55   $38.50  
  Purchase #6 $159.29   7.120%   $170.6314   $170.63   $170.65   $170.60  
  Purchase #7 $97.52   7.481%   $104.8155   $104.82   $104.80   $104.80  
  7 purchase totals = $725.72       $780.3049   $780.31   $780.35   $780.20