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	$112.34	13.350%	$127.3374	$127.34	$127.35	$127.30
Purchase #2	$64.87	3.531%	$67.1606	$67.16	$67.15	$67.20
Purchase #3	$166.63	13.470%	$189.0751	$189.08	$189.10	$189.10
Purchase #4	$150.33	6.241%	$159.7121	$159.71	$159.70	$159.70
Purchase #5	$174.26	6.323%	$185.2785	$185.28	$185.30	$185.30
Purchase #6	$227.54	4.440%	$237.6428	$237.64	$237.65	$237.60
Purchase #7	$144.75	4.244%	$150.8932	$150.89	$150.90	$150.90
7 purchase totals =	$1,040.72		$1,117.0997	$1,117.10	$1,117.15	$1,117.10