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 $219.37   9.227%   $239.6113   $239.61   $239.60   $239.60  
  Purchase #2 $57.50   8.165%   $62.1949   $62.19   $62.20   $62.20  
  Purchase #3 $51.47   12.187%   $57.7426   $57.74   $57.75   $57.70  
  Purchase #4 $6.29   9.224%   $6.8702   $6.87   $6.85   $6.90  
  Purchase #5 $247.27   10.504%   $273.2432   $273.24   $273.25   $273.20  
  Purchase #6 $109.29   5.600%   $115.4102   $115.41   $115.40   $115.40  
  Purchase #7 $202.46   5.817%   $214.2371   $214.24   $214.25   $214.20  
  7 purchase totals = $893.65       $969.3095   $969.30   $969.30   $969.20