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	$100.31	11.856%	$112.2028	$112.20	$112.20	$112.20
Purchase #2	$20.95	4.422%	$21.8764	$21.88	$21.90	$21.90
Purchase #3	$153.84	4.404%	$160.6151	$160.62	$160.60	$160.60
Purchase #4	$50.78	3.503%	$52.5588	$52.56	$52.55	$52.60
Purchase #5	$214.82	9.181%	$234.5426	$234.54	$234.55	$234.50
Purchase #6	$137.46	11.359%	$153.0741	$153.07	$153.05	$153.10
Purchase #7	$112.63	4.136%	$117.2884	$117.29	$117.30	$117.30
7 purchase totals =	$790.79		$852.1582	$852.16	$852.15	$852.20