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 $232.42   6.328%   $247.1275   $247.13   $247.15   $247.10  
  Purchase #2 $158.68   5.770%   $167.8358   $167.84   $167.85   $167.80  
  Purchase #3 $103.45   4.290%   $107.888   $107.89   $107.90   $107.90  
  Purchase #4 $111.84   6.118%   $118.6824   $118.68   $118.70   $118.70  
  Purchase #5 $241.91   4.832%   $253.5991   $253.60   $253.60   $253.60  
  Purchase #6 $112.53   11.193%   $125.1255   $125.13   $125.15   $125.10  
  Purchase #7 $244.47   8.844%   $266.0909   $266.09   $266.10   $266.10  
  7 purchase totals = $1,205.30       $1,286.3492   $1,286.36   $1,286.45   $1,286.30