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	$21.41	11.592%	$23.8918	$23.89	$23.90	$23.90
Purchase #2	$175.54	6.221%	$186.4603	$186.46	$186.45	$186.50
Purchase #3	$160.31	13.611%	$182.1298	$182.13	$182.15	$182.10
Purchase #4	$86.78	13.571%	$98.5569	$98.56	$98.55	$98.60
Purchase #5	$46.94	11.655%	$52.4109	$52.41	$52.40	$52.40
Purchase #6	$228.83	7.296%	$245.5254	$245.53	$245.55	$245.50
Purchase #7	$199.61	4.652%	$208.8959	$208.90	$208.90	$208.90
7 purchase totals =	$919.42		$997.8710	$997.88	$997.90	$997.90