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 $61.61   4.533%   $64.4028   $64.40   $64.40   $64.40  
  Purchase #2 $169.33   13.105%   $191.5207   $191.52   $191.50   $191.50  
  Purchase #3 $223.95   9.804%   $245.9061   $245.91   $245.90   $245.90  
  Purchase #4 $150.98   5.208%   $158.843   $158.84   $158.85   $158.80  
  Purchase #5 $91.64   9.407%   $100.2606   $100.26   $100.25   $100.30  
  Purchase #6 $40.90   9.357%   $44.727   $44.73   $44.75   $44.70  
  Purchase #7 $97.71   8.499%   $106.0144   $106.01   $106.00   $106.00  
  7 purchase totals = $836.12       $911.6746   $911.67   $911.65   $911.60