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	$71.40	10.465%	$78.872	$78.87	$78.85	$78.90
Purchase #2	$26.97	5.306%	$28.401	$28.40	$28.40	$28.40
Purchase #3	$127.42	3.465%	$131.8351	$131.84	$131.85	$131.80
Purchase #4	$33.88	4.113%	$35.2735	$35.27	$35.25	$35.30
Purchase #5	$133.27	10.238%	$146.9142	$146.91	$146.90	$146.90
Purchase #6	$222.82	13.622%	$253.1725	$253.17	$253.15	$253.20
Purchase #7	$190.32	12.674%	$214.4412	$214.44	$214.45	$214.40
7 purchase totals =	$806.08		$888.9095	$888.90	$888.85	$888.90