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 $223.48   11.798%   $249.8462   $249.85   $249.85   $249.80  
  Purchase #2 $146.43   6.214%   $155.5292   $155.53   $155.55   $155.50  
  Purchase #3 $162.28   8.259%   $175.6827   $175.68   $175.70   $175.70  
  Purchase #4 $106.63   8.114%   $115.282   $115.28   $115.30   $115.30  
  Purchase #5 $147.85   6.390%   $157.2976   $157.30   $157.30   $157.30  
  Purchase #6 $224.73   5.646%   $237.4183   $237.42   $237.40   $237.40  
  Purchase #7 $52.81   12.144%   $59.2232   $59.22   $59.20   $59.20  
  7 purchase totals = $1,064.21       $1,150.2792   $1,150.28   $1,150.30   $1,150.20