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	$93.33	12.657%	$105.1428	$105.14	$105.15	$105.10
Purchase #2	$129.61	8.571%	$140.7189	$140.72	$140.70	$140.70
Purchase #3	$202.96	10.712%	$224.7011	$224.70	$224.70	$224.70
Purchase #4	$67.49	4.169%	$70.3037	$70.30	$70.30	$70.30
Purchase #5	$12.75	12.564%	$14.3519	$14.35	$14.35	$14.40
Purchase #6	$89.42	10.790%	$99.0684	$99.07	$99.05	$99.10
Purchase #7	$228.67	4.185%	$238.2398	$238.24	$238.25	$238.20
7 purchase totals =	$824.23		$892.5266	$892.52	$892.50	$892.50