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 $40.84   6.521%   $43.5032   $43.50   $43.50   $43.50  
  Purchase #2 $97.26   7.377%   $104.4349   $104.43   $104.45   $104.40  
  Purchase #3 $71.63   13.394%   $81.2241   $81.22   $81.20   $81.20  
  Purchase #4 $167.64   7.832%   $180.7696   $180.77   $180.75   $180.80  
  Purchase #5 $219.73   12.642%   $247.5083   $247.51   $247.50   $247.50  
  Purchase #6 $48.47   10.725%   $53.6684   $53.67   $53.65   $53.70  
  Purchase #7 $56.82   3.678%   $58.9098   $58.91   $58.90   $58.90  
  7 purchase totals = $702.39       $770.0183   $770.01   $769.95   $770.00