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	$121.67	7.306%	$130.5592	$130.56	$130.55	$130.60
Purchase #2	$227.82	10.230%	$251.126	$251.13	$251.15	$251.10
Purchase #3	$28.42	3.509%	$29.4173	$29.42	$29.40	$29.40
Purchase #4	$51.94	5.476%	$54.7842	$54.78	$54.80	$54.80
Purchase #5	$80.74	11.279%	$89.8467	$89.85	$89.85	$89.80
Purchase #6	$142.67	6.615%	$152.1076	$152.11	$152.10	$152.10
Purchase #7	$31.64	4.628%	$33.1043	$33.10	$33.10	$33.10
7 purchase totals =	$684.90		$740.9453	$740.95	$740.95	$740.90