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 $83.72   12.804%   $94.4395   $94.44   $94.45   $94.40  
  Purchase #2 $131.37   13.176%   $148.6793   $148.68   $148.70   $148.70  
  Purchase #3 $6.62   5.512%   $6.9849   $6.98   $7.00   $7.00  
  Purchase #4 $186.51   4.509%   $194.9197   $194.92   $194.90   $194.90  
  Purchase #5 $240.62   8.705%   $261.566   $261.57   $261.55   $261.60  
  Purchase #6 $119.71   3.462%   $123.8544   $123.85   $123.85   $123.90  
  Purchase #7 $126.81   3.242%   $130.9212   $130.92   $130.90   $130.90  
  7 purchase totals = $895.36       $961.3650   $961.36   $961.35   $961.40