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 $146.74   11.854%   $164.1346   $164.13   $164.15   $164.10  
  Purchase #2 $244.87   9.793%   $268.8501   $268.85   $268.85   $268.90  
  Purchase #3 $91.27   12.592%   $102.7627   $102.76   $102.75   $102.80  
  Purchase #4 $208.48   13.493%   $236.6102   $236.61   $236.60   $236.60  
  Purchase #5 $83.79   11.829%   $93.7015   $93.70   $93.70   $93.70  
  Purchase #6 $51.25   5.178%   $53.9037   $53.90   $53.90   $53.90  
  Purchase #7 $27.48   8.199%   $29.7331   $29.73   $29.75   $29.70  
  7 purchase totals = $853.88       $949.6959   $949.68   $949.70   $949.70