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	$70.77	11.369%	$78.8158	$78.82	$78.80	$78.80
Purchase #2	$70.41	11.227%	$78.3149	$78.31	$78.30	$78.30
Purchase #3	$247.74	6.405%	$263.6077	$263.61	$263.60	$263.60
Purchase #4	$223.42	6.865%	$238.7578	$238.76	$238.75	$238.80
Purchase #5	$136.49	7.456%	$146.6667	$146.67	$146.65	$146.70
Purchase #6	$160.62	11.579%	$179.2182	$179.22	$179.20	$179.20
Purchase #7	$220.80	3.437%	$228.3889	$228.39	$228.40	$228.40
7 purchase totals =	$1,130.25		$1,213.7700	$1,213.78	$1,213.70	$1,213.80