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 $233.38   7.197%   $250.1764   $250.18   $250.20   $250.20  
  Purchase #2 $101.87   13.419%   $115.5399   $115.54   $115.55   $115.50  
  Purchase #3 $51.99   4.398%   $54.2765   $54.28   $54.30   $54.30  
  Purchase #4 $85.81   11.562%   $95.7314   $95.73   $95.75   $95.70  
  Purchase #5 $170.90   3.828%   $177.4421   $177.44   $177.45   $177.40  
  Purchase #6 $246.61   12.316%   $276.9825   $276.98   $277.00   $277.00  
  Purchase #7 $234.28   3.136%   $241.627   $241.63   $241.65   $241.60  
  7 purchase totals = $1,124.84       $1,211.7758   $1,211.78   $1,211.90   $1,211.70