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 $146.95   13.151%   $166.2754   $166.28   $166.30   $166.30  
  Purchase #2 $36.98   11.664%   $41.2933   $41.29   $41.30   $41.30  
  Purchase #3 $56.38   11.219%   $62.7053   $62.71   $62.70   $62.70  
  Purchase #4 $76.53   3.782%   $79.4244   $79.42   $79.40   $79.40  
  Purchase #5 $92.76   3.711%   $96.2023   $96.20   $96.20   $96.20  
  Purchase #6 $81.29   11.170%   $90.3701   $90.37   $90.35   $90.40  
  Purchase #7 $214.25   10.716%   $237.209   $237.21   $237.20   $237.20  
  7 purchase totals = $705.14       $773.4798   $773.48   $773.45   $773.50