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 $242.53   9.153%   $264.7288   $264.73   $264.75   $264.70  
  Purchase #2 $21.90   3.429%   $22.651   $22.65   $22.65   $22.70  
  Purchase #3 $249.90   9.329%   $273.2132   $273.21   $273.20   $273.20  
  Purchase #4 $207.32   12.634%   $233.5128   $233.51   $233.50   $233.50  
  Purchase #5 $68.82   10.231%   $75.861   $75.86   $75.85   $75.90  
  Purchase #6 $218.87   8.361%   $237.1697   $237.17   $237.15   $237.20  
  Purchase #7 $190.44   8.407%   $206.4503   $206.45   $206.45   $206.50  
  7 purchase totals = $1,199.78       $1,313.5868   $1,313.58   $1,313.55   $1,313.70