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 $224.92   7.711%   $242.2636   $242.26   $242.25   $242.30  
  Purchase #2 $242.30   3.312%   $250.325   $250.33   $250.35   $250.30  
  Purchase #3 $43.82   13.554%   $49.7594   $49.76   $49.75   $49.80  
  Purchase #4 $68.58   5.762%   $72.5316   $72.53   $72.55   $72.50  
  Purchase #5 $227.54   12.721%   $256.4854   $256.49   $256.50   $256.50  
  Purchase #6 $164.95   13.370%   $187.0038   $187.00   $187.00   $187.00  
  Purchase #7 $190.69   6.444%   $202.9781   $202.98   $203.00   $203.00  
  7 purchase totals = $1,162.80       $1,261.3469   $1,261.35   $1,261.40   $1,261.40