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	$122.87	3.483%	$127.1496	$127.15	$127.15	$127.10
Purchase #2	$58.99	9.385%	$64.5262	$64.53	$64.55	$64.50
Purchase #3	$169.43	13.197%	$191.7897	$191.79	$191.80	$191.80
Purchase #4	$93.69	7.159%	$100.3973	$100.40	$100.40	$100.40
Purchase #5	$87.87	3.176%	$90.6608	$90.66	$90.65	$90.70
Purchase #6	$78.76	8.413%	$85.3861	$85.39	$85.40	$85.40
Purchase #7	$135.49	11.501%	$151.0727	$151.07	$151.05	$151.10
7 purchase totals =	$747.10		$810.9824	$810.99	$811.00	$811.00