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	$19.46	11.341%	$21.667	$21.67	$21.65	$21.70
Purchase #2	$43.26	13.222%	$48.9798	$48.98	$49.00	$49.00
Purchase #3	$62.83	7.641%	$67.6308	$67.63	$67.65	$67.60
Purchase #4	$83.58	10.332%	$92.2155	$92.22	$92.20	$92.20
Purchase #5	$10.87	5.547%	$11.473	$11.47	$11.45	$11.50
Purchase #6	$175.79	12.707%	$198.1276	$198.13	$198.15	$198.10
Purchase #7	$54.31	12.536%	$61.1183	$61.12	$61.10	$61.10
7 purchase totals =	$450.10		$501.2120	$501.22	$501.20	$501.20