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 $84.91   13.292%   $96.1962   $96.20   $96.20   $96.20  
  Purchase #2 $112.66   11.341%   $125.4368   $125.44   $125.45   $125.40  
  Purchase #3 $154.76   12.676%   $174.3774   $174.38   $174.40   $174.40  
  Purchase #4 $152.49   12.309%   $171.26   $171.26   $171.25   $171.30  
  Purchase #5 $74.69   4.470%   $78.0286   $78.03   $78.05   $78.00  
  Purchase #6 $11.44   12.564%   $12.8773   $12.88   $12.90   $12.90  
  Purchase #7 $26.27   6.775%   $28.0498   $28.05   $28.05   $28.00  
  7 purchase totals = $617.22       $686.2261   $686.24   $686.30   $686.20