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 $232.34   6.529%   $247.5095   $247.51   $247.50   $247.50  
  Purchase #2 $226.42   5.493%   $238.8573   $238.86   $238.85   $238.90  
  Purchase #3 $177.34   8.676%   $192.726   $192.73   $192.75   $192.70  
  Purchase #4 $32.94   6.868%   $35.2023   $35.20   $35.20   $35.20  
  Purchase #5 $30.41   11.321%   $33.8527   $33.85   $33.85   $33.90  
  Purchase #6 $122.43   6.378%   $130.2386   $130.24   $130.25   $130.20  
  Purchase #7 $177.76   9.845%   $195.2605   $195.26   $195.25   $195.30  
  7 purchase totals = $999.64       $1,073.6469   $1,073.65   $1,073.65   $1,073.70