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 $66.48   13.660%   $75.5612   $75.56   $75.55   $75.60  
  Purchase #2 $249.91   3.330%   $258.232   $258.23   $258.25   $258.20  
  Purchase #3 $125.71   11.322%   $139.9429   $139.94   $139.95   $139.90  
  Purchase #4 $231.59   8.392%   $251.025   $251.03   $251.05   $251.00  
  Purchase #5 $104.46   9.203%   $114.0735   $114.07   $114.05   $114.10  
  Purchase #6 $94.96   11.581%   $105.9573   $105.96   $105.95   $106.00  
  Purchase #7 $88.65   12.639%   $99.8545   $99.85   $99.85   $99.90  
  7 purchase totals = $961.76       $1,044.6464   $1,044.64   $1,044.65   $1,044.70