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	$91.28	8.628%	$99.1556	$99.16	$99.15	$99.20
Purchase #2	$111.91	10.637%	$123.8139	$123.81	$123.80	$123.80
Purchase #3	$130.99	7.542%	$140.8693	$140.87	$140.85	$140.90
Purchase #4	$140.31	7.817%	$151.278	$151.28	$151.30	$151.30
Purchase #5	$10.43	10.670%	$11.5429	$11.54	$11.55	$11.50
Purchase #6	$93.25	5.608%	$98.4795	$98.48	$98.50	$98.50
Purchase #7	$234.43	11.325%	$260.9792	$260.98	$261.00	$261.00
7 purchase totals =	$812.60		$886.1184	$886.12	$886.15	$886.20