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 $67.55   11.742%   $75.4817   $75.48   $75.50   $75.50  
  Purchase #2 $119.76   10.805%   $132.7001   $132.70   $132.70   $132.70  
  Purchase #3 $228.61   5.489%   $241.1584   $241.16   $241.15   $241.20  
  Purchase #4 $21.98   9.226%   $24.0079   $24.01   $24.00   $24.00  
  Purchase #5 $69.83   5.714%   $73.8201   $73.82   $73.80   $73.80  
  Purchase #6 $110.92   10.549%   $122.621   $122.62   $122.60   $122.60  
  Purchase #7 $120.66   9.779%   $132.4593   $132.46   $132.45   $132.50  
  7 purchase totals = $739.31       $802.2485   $802.25   $802.20   $802.30