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 $84.62   11.398%   $94.265   $94.27   $94.25   $94.30  
  Purchase #2 $69.43   5.129%   $72.9911   $72.99   $73.00   $73.00  
  Purchase #3 $203.46   5.521%   $214.693   $214.69   $214.70   $214.70  
  Purchase #4 $70.67   9.330%   $77.2635   $77.26   $77.25   $77.30  
  Purchase #5 $52.45   4.117%   $54.6094   $54.61   $54.60   $54.60  
  Purchase #6 $176.42   11.842%   $197.3117   $197.31   $197.30   $197.30  
  Purchase #7 $249.60   4.633%   $261.164   $261.16   $261.15   $261.20  
  7 purchase totals = $906.65       $972.2977   $972.29   $972.25   $972.40