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 $245.80   6.561%   $261.9269   $261.93   $261.95   $261.90  
  Purchase #2 $183.26   10.557%   $202.6068   $202.61   $202.60   $202.60  
  Purchase #3 $47.94   3.660%   $49.6946   $49.69   $49.70   $49.70  
  Purchase #4 $111.42   9.157%   $121.6227   $121.62   $121.60   $121.60  
  Purchase #5 $183.67   8.726%   $199.697   $199.70   $199.70   $199.70  
  Purchase #6 $31.84   4.225%   $33.1852   $33.19   $33.20   $33.20  
  Purchase #7 $87.42   4.283%   $91.1642   $91.16   $91.15   $91.20  
  7 purchase totals = $891.35       $959.8974   $959.90   $959.90   $959.90