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	$24.25	12.283%	$27.2286	$27.23	$27.25	$27.20
Purchase #2	$179.63	9.284%	$196.3068	$196.31	$196.30	$196.30
Purchase #3	$155.61	3.103%	$160.4386	$160.44	$160.45	$160.40
Purchase #4	$106.90	10.839%	$118.4869	$118.49	$118.50	$118.50
Purchase #5	$86.66	5.816%	$91.7001	$91.70	$91.70	$91.70
Purchase #6	$80.69	5.385%	$85.0352	$85.04	$85.05	$85.00
Purchase #7	$223.65	4.422%	$233.5398	$233.54	$233.55	$233.50
7 purchase totals =	$857.39		$912.7360	$912.75	$912.80	$912.60