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	$165.27	5.466%	$174.3037	$174.30	$174.30	$174.30
Purchase #2	$242.45	5.807%	$256.5291	$256.53	$256.55	$256.50
Purchase #3	$214.44	11.188%	$238.4315	$238.43	$238.45	$238.40
Purchase #4	$198.39	12.222%	$222.6372	$222.64	$222.65	$222.60
Purchase #5	$11.72	5.356%	$12.3477	$12.35	$12.35	$12.30
Purchase #6	$149.75	10.863%	$166.0173	$166.02	$166.00	$166.00
Purchase #7	$236.29	10.116%	$260.1931	$260.19	$260.20	$260.20
7 purchase totals =	$1,218.31		$1,330.4596	$1,330.46	$1,330.50	$1,330.30