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	$80.28	11.731%	$89.6976	$89.70	$89.70	$89.70
Purchase #2	$234.35	7.166%	$251.1435	$251.14	$251.15	$251.10
Purchase #3	$65.26	3.285%	$67.4038	$67.40	$67.40	$67.40
Purchase #4	$79.63	12.130%	$89.2891	$89.29	$89.30	$89.30
Purchase #5	$20.76	3.778%	$21.5443	$21.54	$21.55	$21.50
Purchase #6	$142.91	3.295%	$147.6189	$147.62	$147.60	$147.60
Purchase #7	$150.83	6.213%	$160.2011	$160.20	$160.20	$160.20
7 purchase totals =	$774.02		$826.8983	$826.89	$826.90	$826.80