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	$91.38	9.460%	$100.0245	$100.02	$100.00	$100.00
Purchase #2	$147.38	11.491%	$164.3154	$164.32	$164.30	$164.30
Purchase #3	$211.85	10.188%	$233.4333	$233.43	$233.45	$233.40
Purchase #4	$9.86	8.741%	$10.7219	$10.72	$10.70	$10.70
Purchase #5	$164.37	9.793%	$180.4668	$180.47	$180.45	$180.50
Purchase #6	$194.49	5.117%	$204.4421	$204.44	$204.45	$204.40
Purchase #7	$91.49	3.253%	$94.4662	$94.47	$94.45	$94.50
7 purchase totals =	$910.82		$987.8702	$987.87	$987.80	$987.80