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	$124.73	9.594%	$136.6966	$136.70	$136.70	$136.70
Purchase #2	$66.83	13.833%	$76.0746	$76.07	$76.05	$76.10
Purchase #3	$76.62	7.185%	$82.1251	$82.13	$82.15	$82.10
Purchase #4	$153.62	7.713%	$165.4687	$165.47	$165.45	$165.50
Purchase #5	$41.41	13.449%	$46.9792	$46.98	$47.00	$47.00
Purchase #6	$28.88	13.781%	$32.86	$32.86	$32.85	$32.90
Purchase #7	$18.54	8.201%	$20.0605	$20.06	$20.05	$20.10
7 purchase totals =	$510.63		$560.2647	$560.27	$560.25	$560.40