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 $54.89   12.793%   $61.9121   $61.91   $61.90   $61.90  
  Purchase #2 $208.35   7.681%   $224.3534   $224.35   $224.35   $224.40  
  Purchase #3 $141.60   11.235%   $157.5088   $157.51   $157.50   $157.50  
  Purchase #4 $189.73   5.426%   $200.0247   $200.02   $200.00   $200.00  
  Purchase #5 $161.68   5.658%   $170.8279   $170.83   $170.85   $170.80  
  Purchase #6 $112.82   8.161%   $122.0272   $122.03   $122.05   $122.00  
  Purchase #7 $182.98   3.627%   $189.6167   $189.62   $189.60   $189.60  
  7 purchase totals = $1,052.05       $1,126.2708   $1,126.27   $1,126.25   $1,126.20