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 $46.63   12.657%   $52.532   $52.53   $52.55   $52.50  
  Purchase #2 $61.83   7.144%   $66.2471   $66.25   $66.25   $66.20  
  Purchase #3 $84.74   9.692%   $92.953   $92.95   $92.95   $93.00  
  Purchase #4 $24.77   12.214%   $27.7954   $27.80   $27.80   $27.80  
  Purchase #5 $178.43   5.633%   $188.481   $188.48   $188.50   $188.50  
  Purchase #6 $125.97   3.792%   $130.7468   $130.75   $130.75   $130.70  
  Purchase #7 $122.40   8.755%   $133.1161   $133.12   $133.10   $133.10  
  7 purchase totals = $644.77       $691.8714   $691.88   $691.90   $691.80