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	$112.90	10.125%	$124.3311	$124.33	$124.35	$124.30
Purchase #2	$73.51	6.155%	$78.0345	$78.03	$78.05	$78.00
Purchase #3	$127.41	13.479%	$144.5836	$144.58	$144.60	$144.60
Purchase #4	$238.56	5.148%	$250.8411	$250.84	$250.85	$250.80
Purchase #5	$109.55	4.752%	$114.7558	$114.76	$114.75	$114.80
Purchase #6	$201.71	9.380%	$220.6304	$220.63	$220.65	$220.60
Purchase #7	$230.68	7.176%	$247.2336	$247.23	$247.25	$247.20
7 purchase totals =	$1,094.32		$1,180.4101	$1,180.40	$1,180.50	$1,180.30