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 $67.97   11.754%   $75.9592   $75.96   $75.95   $76.00  
  Purchase #2 $244.56   7.151%   $262.0485   $262.05   $262.05   $262.00  
  Purchase #3 $24.50   4.849%   $25.688   $25.69   $25.70   $25.70  
  Purchase #4 $152.59   13.506%   $173.1988   $173.20   $173.20   $173.20  
  Purchase #5 $5.83   6.597%   $6.2146   $6.21   $6.20   $6.20  
  Purchase #6 $128.66   5.520%   $135.762   $135.76   $135.75   $135.80  
  Purchase #7 $226.49   10.616%   $250.5342   $250.53   $250.55   $250.50  
  7 purchase totals = $850.60       $929.4053   $929.40   $929.40   $929.40