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 $104.81   11.670%   $117.0413   $117.04   $117.05   $117.00  
  Purchase #2 $249.36   6.782%   $266.2716   $266.27   $266.25   $266.30  
  Purchase #3 $42.26   12.806%   $47.6718   $47.67   $47.65   $47.70  
  Purchase #4 $34.83   4.332%   $36.3388   $36.34   $36.35   $36.30  
  Purchase #5 $242.46   3.310%   $250.4854   $250.49   $250.50   $250.50  
  Purchase #6 $177.65   11.203%   $197.5521   $197.55   $197.55   $197.60  
  Purchase #7 $49.37   7.312%   $52.9799   $52.98   $53.00   $53.00  
  7 purchase totals = $900.74       $968.3409   $968.34   $968.35   $968.40