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	$50.57	10.435%	$55.847	$55.85	$55.85	$55.80
Purchase #2	$125.74	12.443%	$141.3858	$141.39	$141.40	$141.40
Purchase #3	$175.89	8.242%	$190.3869	$190.39	$190.40	$190.40
Purchase #4	$41.60	6.422%	$44.2716	$44.27	$44.25	$44.30
Purchase #5	$76.28	13.194%	$86.3444	$86.34	$86.35	$86.30
Purchase #6	$219.82	9.502%	$240.7073	$240.71	$240.70	$240.70
Purchase #7	$92.33	4.312%	$96.3113	$96.31	$96.30	$96.30
7 purchase totals =	$782.23		$855.2543	$855.26	$855.25	$855.20