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	$48.74	11.786%	$54.4845	$54.48	$54.50	$54.50
Purchase #2	$172.92	13.843%	$196.8573	$196.86	$196.85	$196.90
Purchase #3	$48.63	13.160%	$55.0297	$55.03	$55.05	$55.00
Purchase #4	$173.63	7.308%	$186.3189	$186.32	$186.30	$186.30
Purchase #5	$152.67	12.460%	$171.6927	$171.69	$171.70	$171.70
Purchase #6	$32.28	11.158%	$35.8818	$35.88	$35.90	$35.90
Purchase #7	$21.65	4.447%	$22.6128	$22.61	$22.60	$22.60
7 purchase totals =	$650.52		$722.8777	$722.87	$722.90	$722.90