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 $64.59   7.495%   $69.431   $69.43   $69.45   $69.40  
  Purchase #2 $86.94   12.163%   $97.5145   $97.51   $97.50   $97.50  
  Purchase #3 $165.66   3.111%   $170.8137   $170.81   $170.80   $170.80  
  Purchase #4 $125.28   8.742%   $136.232   $136.23   $136.25   $136.20  
  Purchase #5 $143.67   10.226%   $158.3617   $158.36   $158.35   $158.40  
  Purchase #6 $184.63   5.546%   $194.8696   $194.87   $194.85   $194.90  
  Purchase #7 $155.37   13.250%   $175.9565   $175.96   $175.95   $176.00  
  7 purchase totals = $926.14       $1,003.1790   $1,003.17   $1,003.15   $1,003.20