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	$25.38	11.448%	$28.2855	$28.29	$28.30	$28.30
Purchase #2	$39.98	13.864%	$45.5228	$45.52	$45.50	$45.50
Purchase #3	$18.43	8.104%	$19.9236	$19.92	$19.90	$19.90
Purchase #4	$68.63	3.774%	$71.2201	$71.22	$71.20	$71.20
Purchase #5	$228.27	13.431%	$258.9289	$258.93	$258.95	$258.90
Purchase #6	$247.70	11.341%	$275.7917	$275.79	$275.80	$275.80
Purchase #7	$211.47	5.268%	$222.6102	$222.61	$222.60	$222.60
7 purchase totals =	$839.86		$922.2828	$922.28	$922.25	$922.20