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	$155.53	9.807%	$170.7828	$170.78	$170.80	$170.80
Purchase #2	$132.85	6.583%	$141.5955	$141.60	$141.60	$141.60
Purchase #3	$134.69	9.685%	$147.7347	$147.73	$147.75	$147.70
Purchase #4	$173.30	8.625%	$188.2471	$188.25	$188.25	$188.20
Purchase #5	$200.57	11.497%	$223.6295	$223.63	$223.65	$223.60
Purchase #6	$141.87	12.368%	$159.4165	$159.42	$159.40	$159.40
Purchase #7	$32.56	4.873%	$34.1466	$34.15	$34.15	$34.10
7 purchase totals =	$971.37		$1,065.5527	$1,065.56	$1,065.60	$1,065.40