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	$150.58	13.256%	$170.5409	$170.54	$170.55	$170.50
Purchase #2	$18.31	13.148%	$20.7174	$20.72	$20.70	$20.70
Purchase #3	$99.58	3.535%	$103.1002	$103.10	$103.10	$103.10
Purchase #4	$87.91	3.256%	$90.7723	$90.77	$90.75	$90.80
Purchase #5	$61.42	4.613%	$64.2533	$64.25	$64.25	$64.30
Purchase #6	$217.78	5.445%	$229.6381	$229.64	$229.65	$229.60
Purchase #7	$71.66	9.866%	$78.73	$78.73	$78.75	$78.70
7 purchase totals =	$707.24		$757.7522	$757.75	$757.75	$757.70