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	$247.73	8.292%	$268.2718	$268.27	$268.25	$268.30
Purchase #2	$204.65	4.224%	$213.2944	$213.29	$213.30	$213.30
Purchase #3	$5.48	12.313%	$6.1548	$6.15	$6.15	$6.20
Purchase #4	$114.73	11.457%	$127.8746	$127.87	$127.85	$127.90
Purchase #5	$78.44	13.103%	$88.718	$88.72	$88.70	$88.70
Purchase #6	$38.45	5.452%	$40.5463	$40.55	$40.55	$40.50
Purchase #7	$39.55	10.543%	$43.7198	$43.72	$43.70	$43.70
7 purchase totals =	$729.03		$788.5797	$788.57	$788.50	$788.60