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	$127.63	6.783%	$136.2871	$136.29	$136.30	$136.30
Purchase #2	$178.72	11.812%	$199.8304	$199.83	$199.85	$199.80
Purchase #3	$227.58	6.810%	$243.0782	$243.08	$243.10	$243.10
Purchase #4	$99.71	3.326%	$103.0264	$103.03	$103.05	$103.00
Purchase #5	$152.52	12.359%	$171.3699	$171.37	$171.35	$171.40
Purchase #6	$50.87	5.136%	$53.4827	$53.48	$53.50	$53.50
Purchase #7	$83.69	5.215%	$88.0544	$88.05	$88.05	$88.10
7 purchase totals =	$920.72		$995.1291	$995.13	$995.20	$995.20