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	$24.28	9.678%	$26.6298	$26.63	$26.65	$26.60
Purchase #2	$71.88	8.806%	$78.2098	$78.21	$78.20	$78.20
Purchase #3	$238.77	13.113%	$270.0799	$270.08	$270.10	$270.10
Purchase #4	$136.62	4.281%	$142.4687	$142.47	$142.45	$142.50
Purchase #5	$176.32	9.171%	$192.4903	$192.49	$192.50	$192.50
Purchase #6	$42.89	5.510%	$45.2532	$45.25	$45.25	$45.30
Purchase #7	$33.99	9.708%	$37.2897	$37.29	$37.30	$37.30
7 purchase totals =	$724.75		$792.4214	$792.42	$792.45	$792.50