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 $57.27   8.531%   $62.1557   $62.16   $62.15   $62.20  
  Purchase #2 $96.41   5.300%   $101.5197   $101.52   $101.50   $101.50  
  Purchase #3 $64.99   8.368%   $70.4284   $70.43   $70.45   $70.40  
  Purchase #4 $24.92   9.695%   $27.336   $27.34   $27.35   $27.30  
  Purchase #5 $141.54   10.382%   $156.2347   $156.23   $156.25   $156.20  
  Purchase #6 $207.88   8.843%   $226.2628   $226.26   $226.25   $226.30  
  Purchase #7 $116.77   7.555%   $125.592   $125.59   $125.60   $125.60  
  7 purchase totals = $709.78       $769.5293   $769.53   $769.55   $769.50