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	$42.72	6.563%	$45.5237	$45.52	$45.50	$45.50
Purchase #2	$215.95	3.424%	$223.3441	$223.34	$223.35	$223.30
Purchase #3	$55.68	12.666%	$62.7324	$62.73	$62.75	$62.70
Purchase #4	$49.76	7.572%	$53.5278	$53.53	$53.55	$53.50
Purchase #5	$220.77	4.558%	$230.8327	$230.83	$230.85	$230.80
Purchase #6	$33.75	11.781%	$37.7261	$37.73	$37.75	$37.70
Purchase #7	$28.31	4.348%	$29.5409	$29.54	$29.55	$29.50
7 purchase totals =	$646.94		$683.2277	$683.22	$683.30	$683.00