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 $21.62   9.302%   $23.6311   $23.63   $23.65   $23.60  
  Purchase #2 $137.68   7.184%   $147.5709   $147.57   $147.55   $147.60  
  Purchase #3 $42.43   12.638%   $47.7923   $47.79   $47.80   $47.80  
  Purchase #4 $210.30   6.464%   $223.8938   $223.89   $223.90   $223.90  
  Purchase #5 $118.97   5.413%   $125.4098   $125.41   $125.40   $125.40  
  Purchase #6 $183.63   12.755%   $207.052   $207.05   $207.05   $207.10  
  Purchase #7 $51.55   3.605%   $53.4084   $53.41   $53.40   $53.40  
  7 purchase totals = $766.18       $828.7583   $828.75   $828.75   $828.80