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 $225.69   10.112%   $248.5118   $248.51   $248.50   $248.50  
  Purchase #2 $215.38   11.215%   $239.5349   $239.53   $239.55   $239.50  
  Purchase #3 $65.58   3.796%   $68.0694   $68.07   $68.05   $68.10  
  Purchase #4 $235.86   11.425%   $262.807   $262.81   $262.80   $262.80  
  Purchase #5 $144.84   9.338%   $158.3652   $158.37   $158.35   $158.40  
  Purchase #6 $93.63   4.489%   $97.8331   $97.83   $97.85   $97.80  
  Purchase #7 $217.52   9.514%   $238.2149   $238.21   $238.20   $238.20  
  7 purchase totals = $1,198.50       $1,313.3363   $1,313.33   $1,313.30   $1,313.30