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	$128.77	7.738%	$138.7342	$138.73	$138.75	$138.70
Purchase #2	$73.60	9.159%	$80.341	$80.34	$80.35	$80.30
Purchase #3	$47.95	6.643%	$51.1353	$51.14	$51.15	$51.10
Purchase #4	$51.74	5.482%	$54.5764	$54.58	$54.60	$54.60
Purchase #5	$186.30	7.224%	$199.7583	$199.76	$199.75	$199.80
Purchase #6	$82.92	8.402%	$89.8869	$89.89	$89.90	$89.90
Purchase #7	$95.45	11.812%	$106.7246	$106.72	$106.70	$106.70
7 purchase totals =	$666.73		$721.1567	$721.16	$721.20	$721.10