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	$10.33	13.490%	$11.7235	$11.72	$11.70	$11.70
Purchase #2	$99.31	4.339%	$103.6191	$103.62	$103.60	$103.60
Purchase #3	$85.32	6.627%	$90.9742	$90.97	$90.95	$91.00
Purchase #4	$67.76	6.717%	$72.3114	$72.31	$72.30	$72.30
Purchase #5	$95.79	9.727%	$105.1075	$105.11	$105.10	$105.10
Purchase #6	$95.95	7.572%	$103.2153	$103.22	$103.20	$103.20
Purchase #7	$239.42	10.548%	$264.674	$264.67	$264.65	$264.70
7 purchase totals =	$693.88		$751.6250	$751.62	$751.50	$751.60