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 $60.57   3.648%   $62.7796   $62.78   $62.80   $62.80  
  Purchase #2 $31.80   12.391%   $35.7403   $35.74   $35.75   $35.70  
  Purchase #3 $234.28   13.105%   $264.9824   $264.98   $265.00   $265.00  
  Purchase #4 $56.38   7.856%   $60.8092   $60.81   $60.80   $60.80  
  Purchase #5 $137.67   7.185%   $147.5616   $147.56   $147.55   $147.60  
  Purchase #6 $218.31   13.847%   $248.5394   $248.54   $248.55   $248.50  
  Purchase #7 $118.81   10.626%   $131.4348   $131.43   $131.45   $131.40  
  7 purchase totals = $857.82       $951.8473   $951.84   $951.90   $951.80