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	$14.90	5.733%	$15.7542	$15.75	$15.75	$15.80
Purchase #2	$153.67	11.259%	$170.9717	$170.97	$170.95	$171.00
Purchase #3	$79.34	7.314%	$85.1429	$85.14	$85.15	$85.10
Purchase #4	$86.63	4.566%	$90.5855	$90.59	$90.60	$90.60
Purchase #5	$37.83	4.399%	$39.4941	$39.49	$39.50	$39.50
Purchase #6	$184.32	12.550%	$207.4522	$207.45	$207.45	$207.50
Purchase #7	$32.34	9.283%	$35.3421	$35.34	$35.35	$35.30
7 purchase totals =	$589.03		$644.7427	$644.73	$644.75	$644.80