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 $9.97   10.650%   $11.0318   $11.03   $11.05   $11.00  
  Purchase #2 $125.40   8.569%   $136.1455   $136.15   $136.15   $136.10  
  Purchase #3 $248.76   8.148%   $269.029   $269.03   $269.05   $269.00  
  Purchase #4 $60.34   12.665%   $67.9821   $67.98   $68.00   $68.00  
  Purchase #5 $236.37   3.821%   $245.4017   $245.40   $245.40   $245.40  
  Purchase #6 $158.88   7.584%   $170.9295   $170.93   $170.95   $170.90  
  Purchase #7 $115.46   7.226%   $123.8031   $123.80   $123.80   $123.80  
  7 purchase totals = $955.18       $1,024.3227   $1,024.32   $1,024.40   $1,024.20