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	$173.89	6.561%	$185.2989	$185.30	$185.30	$185.30
Purchase #2	$85.89	5.640%	$90.7342	$90.73	$90.75	$90.70
Purchase #3	$18.27	8.567%	$19.8352	$19.84	$19.85	$19.80
Purchase #4	$82.52	4.276%	$86.0486	$86.05	$86.05	$86.00
Purchase #5	$113.42	12.266%	$127.3321	$127.33	$127.35	$127.30
Purchase #6	$66.31	10.426%	$73.2235	$73.22	$73.20	$73.20
Purchase #7	$90.94	10.734%	$100.7015	$100.70	$100.70	$100.70
7 purchase totals =	$631.24		$683.1740	$683.17	$683.20	$683.00