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 $224.26   11.800%   $250.7227   $250.72   $250.70   $250.70  
  Purchase #2 $164.63   7.230%   $176.5327   $176.53   $176.55   $176.50  
  Purchase #3 $170.84   11.376%   $190.2748   $190.27   $190.25   $190.30  
  Purchase #4 $250.34   5.613%   $264.3916   $264.39   $264.40   $264.40  
  Purchase #5 $49.25   10.362%   $54.3533   $54.35   $54.35   $54.40  
  Purchase #6 $209.68   12.177%   $235.2127   $235.21   $235.20   $235.20  
  Purchase #7 $124.53   8.529%   $135.1512   $135.15   $135.15   $135.20  
  7 purchase totals = $1,193.53       $1,306.6390   $1,306.62   $1,306.60   $1,306.70