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	$39.80	13.826%	$45.3027	$45.30	$45.30	$45.30
Purchase #2	$73.30	6.756%	$78.2521	$78.25	$78.25	$78.30
Purchase #3	$176.83	7.472%	$190.0427	$190.04	$190.05	$190.00
Purchase #4	$17.46	4.658%	$18.2733	$18.27	$18.25	$18.30
Purchase #5	$35.57	8.504%	$38.5949	$38.59	$38.60	$38.60
Purchase #6	$60.36	3.428%	$62.4291	$62.43	$62.45	$62.40
Purchase #7	$219.32	13.272%	$248.4282	$248.43	$248.45	$248.40
7 purchase totals =	$622.64		$681.3230	$681.31	$681.35	$681.30