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 $41.37   4.870%   $43.3847   $43.38   $43.40   $43.40  
  Purchase #2 $191.93   7.353%   $206.0426   $206.04   $206.05   $206.00  
  Purchase #3 $59.25   5.243%   $62.3565   $62.36   $62.35   $62.40  
  Purchase #4 $132.33   3.147%   $136.4944   $136.49   $136.50   $136.50  
  Purchase #5 $28.72   7.767%   $30.9507   $30.95   $30.95   $31.00  
  Purchase #6 $237.78   6.416%   $253.036   $253.04   $253.05   $253.00  
  Purchase #7 $27.34   3.317%   $28.2469   $28.25   $28.25   $28.20  
  7 purchase totals = $718.72       $760.5118   $760.51   $760.55   $760.50