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 $72.61   4.159%   $75.6298   $75.63   $75.65   $75.60  
  Purchase #2 $66.62   8.586%   $72.34   $72.34   $72.35   $72.30  
  Purchase #3 $231.30   4.462%   $241.6206   $241.62   $241.60   $241.60  
  Purchase #4 $105.40   8.574%   $114.437   $114.44   $114.45   $114.40  
  Purchase #5 $229.75   5.667%   $242.7699   $242.77   $242.75   $242.80  
  Purchase #6 $167.79   9.815%   $184.2586   $184.26   $184.25   $184.30  
  Purchase #7 $62.58   12.739%   $70.5521   $70.55   $70.55   $70.60  
  7 purchase totals = $936.05       $1,001.6080   $1,001.61   $1,001.60   $1,001.60