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	$52.83	12.240%	$59.2964	$59.30	$59.30	$59.30
Purchase #2	$153.39	7.588%	$165.0292	$165.03	$165.05	$165.00
Purchase #3	$162.27	13.839%	$184.7265	$184.73	$184.75	$184.70
Purchase #4	$135.76	7.867%	$146.4402	$146.44	$146.45	$146.40
Purchase #5	$209.73	5.295%	$220.8352	$220.84	$220.85	$220.80
Purchase #6	$165.34	5.863%	$175.0339	$175.03	$175.05	$175.00
Purchase #7	$127.72	5.233%	$134.4036	$134.40	$134.40	$134.40
7 purchase totals =	$1,007.04		$1,085.7650	$1,085.77	$1,085.85	$1,085.60