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 $116.68   8.506%   $126.6048   $126.60   $126.60   $126.60  
  Purchase #2 $11.96   8.178%   $12.9381   $12.94   $12.95   $12.90  
  Purchase #3 $236.55   6.151%   $251.1002   $251.10   $251.10   $251.10  
  Purchase #4 $110.37   6.836%   $117.9149   $117.91   $117.90   $117.90  
  Purchase #5 $187.78   5.116%   $197.3868   $197.39   $197.40   $197.40  
  Purchase #6 $136.45   3.105%   $140.6868   $140.69   $140.70   $140.70  
  Purchase #7 $101.43   8.159%   $109.7057   $109.71   $109.70   $109.70  
  7 purchase totals = $901.22       $956.3373   $956.34   $956.35   $956.30