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	$236.51	13.521%	$268.4885	$268.49	$268.50	$268.50
Purchase #2	$113.63	4.221%	$118.4263	$118.43	$118.45	$118.40
Purchase #3	$205.56	8.672%	$223.3862	$223.39	$223.40	$223.40
Purchase #4	$186.83	13.198%	$211.4878	$211.49	$211.50	$211.50
Purchase #5	$151.34	9.465%	$165.6643	$165.66	$165.65	$165.70
Purchase #6	$166.33	4.189%	$173.2976	$173.30	$173.30	$173.30
Purchase #7	$25.87	4.843%	$27.1229	$27.12	$27.10	$27.10
7 purchase totals =	$1,086.07		$1,187.8736	$1,187.88	$1,187.90	$1,187.90