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	$49.28	8.220%	$53.3308	$53.33	$53.35	$53.30
Purchase #2	$56.68	5.627%	$59.8694	$59.87	$59.85	$59.90
Purchase #3	$138.90	4.713%	$145.4464	$145.45	$145.45	$145.40
Purchase #4	$188.93	12.433%	$212.4197	$212.42	$212.40	$212.40
Purchase #5	$28.42	3.179%	$29.3235	$29.32	$29.30	$29.30
Purchase #6	$147.49	7.279%	$158.2258	$158.23	$158.25	$158.20
Purchase #7	$130.49	12.369%	$146.6303	$146.63	$146.65	$146.60
7 purchase totals =	$740.19		$805.2459	$805.25	$805.25	$805.10