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 $239.86   11.799%   $268.1611   $268.16   $268.15   $268.20  
  Purchase #2 $236.46   5.352%   $249.1153   $249.12   $249.10   $249.10  
  Purchase #3 $65.37   10.485%   $72.224   $72.22   $72.20   $72.20  
  Purchase #4 $110.27   6.385%   $117.3107   $117.31   $117.30   $117.30  
  Purchase #5 $241.47   4.763%   $252.9712   $252.97   $252.95   $253.00  
  Purchase #6 $51.79   4.407%   $54.0724   $54.07   $54.05   $54.10  
  Purchase #7 $47.59   13.255%   $53.8981   $53.90   $53.90   $53.90  
  7 purchase totals = $992.81       $1,067.7528   $1,067.75   $1,067.65   $1,067.80