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 $152.97   8.695%   $166.2707   $166.27   $166.25   $166.30  
  Purchase #2 $15.55   11.803%   $17.3854   $17.39   $17.40   $17.40  
  Purchase #3 $234.40   6.637%   $249.9571   $249.96   $249.95   $250.00  
  Purchase #4 $94.30   9.730%   $103.4754   $103.48   $103.50   $103.50  
  Purchase #5 $111.73   3.363%   $115.4875   $115.49   $115.50   $115.50  
  Purchase #6 $168.60   9.617%   $184.8143   $184.81   $184.80   $184.80  
  Purchase #7 $94.87   13.264%   $107.4536   $107.45   $107.45   $107.50  
  7 purchase totals = $872.42       $944.8440   $944.85   $944.85   $945.00