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	$113.69	12.390%	$127.7762	$127.78	$127.80	$127.80
Purchase #2	$137.98	8.736%	$150.0339	$150.03	$150.05	$150.00
Purchase #3	$33.42	6.487%	$35.588	$35.59	$35.60	$35.60
Purchase #4	$156.87	10.482%	$173.3131	$173.31	$173.30	$173.30
Purchase #5	$30.34	10.741%	$33.5988	$33.60	$33.60	$33.60
Purchase #6	$125.43	4.404%	$130.9539	$130.95	$130.95	$131.00
Purchase #7	$115.97	5.773%	$122.6649	$122.66	$122.65	$122.70
7 purchase totals =	$713.70		$773.9288	$773.92	$773.95	$774.00