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 $36.72   13.273%   $41.5938   $41.59   $41.60   $41.60  
  Purchase #2 $214.30   10.216%   $236.1929   $236.19   $236.20   $236.20  
  Purchase #3 $126.84   7.277%   $136.0701   $136.07   $136.05   $136.10  
  Purchase #4 $203.75   11.680%   $227.548   $227.55   $227.55   $227.50  
  Purchase #5 $13.39   6.702%   $14.2874   $14.29   $14.30   $14.30  
  Purchase #6 $142.51   10.653%   $157.6916   $157.69   $157.70   $157.70  
  Purchase #7 $227.74   5.600%   $240.4934   $240.49   $240.50   $240.50  
  7 purchase totals = $965.25       $1,053.8772   $1,053.87   $1,053.90   $1,053.90