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	$32.60	11.714%	$36.4188	$36.42	$36.40	$36.40
Purchase #2	$162.36	6.335%	$172.6455	$172.65	$172.65	$172.60
Purchase #3	$104.67	6.357%	$111.3239	$111.32	$111.30	$111.30
Purchase #4	$75.31	8.260%	$81.5306	$81.53	$81.55	$81.50
Purchase #5	$64.35	10.773%	$71.2824	$71.28	$71.30	$71.30
Purchase #6	$140.94	4.628%	$147.4627	$147.46	$147.45	$147.50
Purchase #7	$153.95	8.308%	$166.7402	$166.74	$166.75	$166.70
7 purchase totals =	$734.18		$787.4041	$787.40	$787.40	$787.30