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	$155.56	13.335%	$176.3039	$176.30	$176.30	$176.30
Purchase #2	$250.43	9.676%	$274.6616	$274.66	$274.65	$274.70
Purchase #3	$49.53	9.379%	$54.1754	$54.18	$54.20	$54.20
Purchase #4	$26.88	6.714%	$28.6847	$28.68	$28.70	$28.70
Purchase #5	$37.88	4.694%	$39.6581	$39.66	$39.65	$39.70
Purchase #6	$172.73	13.506%	$196.0589	$196.06	$196.05	$196.10
Purchase #7	$78.59	5.252%	$82.7175	$82.72	$82.70	$82.70
7 purchase totals =	$771.60		$852.2601	$852.26	$852.25	$852.40