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 $227.40   12.858%   $256.6391   $256.64   $256.65   $256.60  
  Purchase #2 $23.83   11.222%   $26.5042   $26.50   $26.50   $26.50  
  Purchase #3 $221.95   3.567%   $229.867   $229.87   $229.85   $229.90  
  Purchase #4 $164.68   10.743%   $182.3716   $182.37   $182.35   $182.40  
  Purchase #5 $74.39   11.316%   $82.808   $82.81   $82.80   $82.80  
  Purchase #6 $136.59   11.689%   $152.556   $152.56   $152.55   $152.60  
  Purchase #7 $125.45   3.530%   $129.8784   $129.88   $129.90   $129.90  
  7 purchase totals = $974.29       $1,060.6243   $1,060.63   $1,060.60   $1,060.70