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 $84.59   9.603%   $92.7132   $92.71   $92.70   $92.70  
  Purchase #2 $237.93   9.260%   $259.9623   $259.96   $259.95   $260.00  
  Purchase #3 $239.83   9.562%   $262.7625   $262.76   $262.75   $262.80  
  Purchase #4 $177.77   6.169%   $188.7366   $188.74   $188.75   $188.70  
  Purchase #5 $24.59   6.579%   $26.2078   $26.21   $26.20   $26.20  
  Purchase #6 $148.95   13.814%   $169.526   $169.53   $169.55   $169.50  
  Purchase #7 $244.91   3.602%   $253.7317   $253.73   $253.75   $253.70  
  7 purchase totals = $1,158.57       $1,253.6401   $1,253.64   $1,253.65   $1,253.60