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	$238.65	7.168%	$255.7564	$255.76	$255.75	$255.80
Purchase #2	$123.92	6.409%	$131.862	$131.86	$131.85	$131.90
Purchase #3	$128.45	12.846%	$144.9507	$144.95	$144.95	$145.00
Purchase #4	$217.74	12.571%	$245.1121	$245.11	$245.10	$245.10
Purchase #5	$101.63	8.658%	$110.4291	$110.43	$110.45	$110.40
Purchase #6	$202.35	6.172%	$214.839	$214.84	$214.85	$214.80
Purchase #7	$105.38	12.461%	$118.5114	$118.51	$118.50	$118.50
7 purchase totals =	$1,118.12		$1,221.4607	$1,221.46	$1,221.45	$1,221.50