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	$227.58	6.427%	$242.2066	$242.21	$242.20	$242.20
Purchase #2	$250.91	12.392%	$282.0028	$282.00	$282.00	$282.00
Purchase #3	$166.39	11.489%	$185.5065	$185.51	$185.50	$185.50
Purchase #4	$233.82	8.313%	$253.2575	$253.26	$253.25	$253.30
Purchase #5	$190.65	3.201%	$196.7527	$196.75	$196.75	$196.80
Purchase #6	$11.60	4.480%	$12.1197	$12.12	$12.10	$12.10
Purchase #7	$107.34	10.780%	$118.9113	$118.91	$118.90	$118.90
7 purchase totals =	$1,188.29		$1,290.7571	$1,290.76	$1,290.70	$1,290.80