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 $237.74   11.778%   $265.741   $265.74   $265.75   $265.70  
  Purchase #2 $51.55   3.184%   $53.1914   $53.19   $53.20   $53.20  
  Purchase #3 $225.34   5.371%   $237.443   $237.44   $237.45   $237.40  
  Purchase #4 $85.90   10.214%   $94.6738   $94.67   $94.65   $94.70  
  Purchase #5 $205.66   3.535%   $212.9301   $212.93   $212.95   $212.90  
  Purchase #6 $19.50   12.419%   $21.9217   $21.92   $21.90   $21.90  
  Purchase #7 $114.84   4.105%   $119.5542   $119.55   $119.55   $119.60  
  7 purchase totals = $940.53       $1,005.4552   $1,005.44   $1,005.45   $1,005.40