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 $137.65   10.811%   $152.5313   $152.53   $152.55   $152.50  
  Purchase #2 $34.35   3.197%   $35.4482   $35.45   $35.45   $35.40  
  Purchase #3 $168.60   9.707%   $184.966   $184.97   $184.95   $185.00  
  Purchase #4 $158.38   3.578%   $164.0468   $164.05   $164.05   $164.00  
  Purchase #5 $117.82   12.630%   $132.7007   $132.70   $132.70   $132.70  
  Purchase #6 $36.87   3.202%   $38.0506   $38.05   $38.05   $38.10  
  Purchase #7 $232.34   6.508%   $247.4607   $247.46   $247.45   $247.50  
  7 purchase totals = $886.01       $955.2043   $955.21   $955.20   $955.20