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 $68.27   8.353%   $73.9726   $73.97   $73.95   $74.00  
  Purchase #2 $87.75   4.154%   $91.3951   $91.40   $91.40   $91.40  
  Purchase #3 $23.34   5.820%   $24.6984   $24.70   $24.70   $24.70  
  Purchase #4 $244.61   12.684%   $275.6363   $275.64   $275.65   $275.60  
  Purchase #5 $133.60   5.723%   $141.2459   $141.25   $141.25   $141.20  
  Purchase #6 $220.89   8.376%   $239.3917   $239.39   $239.40   $239.40  
  Purchase #7 $61.68   9.290%   $67.4101   $67.41   $67.40   $67.40  
  7 purchase totals = $840.14       $913.7501   $913.76   $913.75   $913.70