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	$122.55	8.866%	$133.4153	$133.42	$133.40	$133.40
Purchase #2	$60.53	6.607%	$64.5292	$64.53	$64.55	$64.50
Purchase #3	$231.92	10.442%	$256.1371	$256.14	$256.15	$256.10
Purchase #4	$178.89	6.358%	$190.2638	$190.26	$190.25	$190.30
Purchase #5	$44.75	5.683%	$47.2931	$47.29	$47.30	$47.30
Purchase #6	$187.62	8.674%	$203.8942	$203.89	$203.90	$203.90
Purchase #7	$94.58	9.793%	$103.8422	$103.84	$103.85	$103.80
7 purchase totals =	$920.84		$999.3749	$999.37	$999.40	$999.30