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 $99.33   4.329%   $103.63   $103.63   $103.65   $103.60  
  Purchase #2 $217.46   6.451%   $231.4883   $231.49   $231.50   $231.50  
  Purchase #3 $63.52   10.726%   $70.3332   $70.33   $70.35   $70.30  
  Purchase #4 $87.99   7.222%   $94.3446   $94.34   $94.35   $94.30  
  Purchase #5 $143.28   13.102%   $162.0525   $162.05   $162.05   $162.10  
  Purchase #6 $70.85   9.120%   $77.3115   $77.31   $77.30   $77.30  
  Purchase #7 $178.69   12.258%   $200.5938   $200.59   $200.60   $200.60  
  7 purchase totals = $861.12       $939.7539   $939.74   $939.80   $939.70