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 $67.61   11.794%   $75.5839   $75.58   $75.60   $75.60  
  Purchase #2 $33.99   8.781%   $36.9747   $36.97   $36.95   $37.00  
  Purchase #3 $248.31   6.265%   $263.8666   $263.87   $263.85   $263.90  
  Purchase #4 $5.91   5.472%   $6.2334   $6.23   $6.25   $6.20  
  Purchase #5 $149.40   6.211%   $158.6792   $158.68   $158.70   $158.70  
  Purchase #6 $200.67   12.314%   $225.3805   $225.38   $225.40   $225.40  
  Purchase #7 $5.94   8.763%   $6.4605   $6.46   $6.45   $6.50  
  7 purchase totals = $711.83       $773.1788   $773.17   $773.20   $773.30