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 $228.94   8.867%   $249.2401   $249.24   $249.25   $249.20  
  Purchase #2 $108.61   10.304%   $119.8012   $119.80   $119.80   $119.80  
  Purchase #3 $219.25   5.211%   $230.6751   $230.68   $230.70   $230.70  
  Purchase #4 $52.42   3.443%   $54.2248   $54.22   $54.20   $54.20  
  Purchase #5 $177.36   11.301%   $197.4035   $197.40   $197.40   $197.40  
  Purchase #6 $243.48   11.873%   $272.3884   $272.39   $272.40   $272.40  
  Purchase #7 $12.87   9.338%   $14.0718   $14.07   $14.05   $14.10  
  7 purchase totals = $1,042.93       $1,137.8049   $1,137.80   $1,137.80   $1,137.80