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 $239.52   12.592%   $269.6804   $269.68   $269.70   $269.70  
  Purchase #2 $158.88   11.248%   $176.7508   $176.75   $176.75   $176.80  
  Purchase #3 $97.75   4.228%   $101.8829   $101.88   $101.90   $101.90  
  Purchase #4 $76.92   7.607%   $82.7713   $82.77   $82.75   $82.80  
  Purchase #5 $33.78   10.313%   $37.2637   $37.26   $37.25   $37.30  
  Purchase #6 $168.97   3.113%   $174.23   $174.23   $174.25   $174.20  
  Purchase #7 $14.48   11.142%   $16.0934   $16.09   $16.10   $16.10  
  7 purchase totals = $790.30       $858.6725   $858.66   $858.70   $858.80