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	$145.83	6.729%	$155.6429	$155.64	$155.65	$155.60
Purchase #2	$37.42	12.311%	$42.0268	$42.03	$42.05	$42.00
Purchase #3	$215.94	13.837%	$245.8196	$245.82	$245.80	$245.80
Purchase #4	$236.74	4.165%	$246.6002	$246.60	$246.60	$246.60
Purchase #5	$50.57	9.362%	$55.3044	$55.30	$55.30	$55.30
Purchase #6	$173.38	10.226%	$191.1098	$191.11	$191.10	$191.10
Purchase #7	$14.63	3.461%	$15.1363	$15.14	$15.15	$15.10
7 purchase totals =	$874.51		$951.6400	$951.64	$951.65	$951.50