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 $33.68   11.413%   $37.5239   $37.52   $37.50   $37.50  
  Purchase #2 $178.76   9.337%   $195.4508   $195.45   $195.45   $195.50  
  Purchase #3 $226.60   4.265%   $236.2645   $236.26   $236.25   $236.30  
  Purchase #4 $90.45   5.322%   $95.2637   $95.26   $95.25   $95.30  
  Purchase #5 $244.98   9.837%   $269.0787   $269.08   $269.10   $269.10  
  Purchase #6 $27.42   5.550%   $28.9418   $28.94   $28.95   $28.90  
  Purchase #7 $90.47   7.569%   $97.3177   $97.32   $97.30   $97.30  
  7 purchase totals = $892.36       $959.8411   $959.83   $959.80   $959.90