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	$170.32	9.105%	$185.8276	$185.83	$185.85	$185.80
Purchase #2	$146.84	12.409%	$165.0614	$165.06	$165.05	$165.10
Purchase #3	$45.73	9.707%	$50.169	$50.17	$50.15	$50.20
Purchase #4	$191.59	7.656%	$206.2581	$206.26	$206.25	$206.30
Purchase #5	$129.85	12.535%	$146.1267	$146.13	$146.15	$146.10
Purchase #6	$9.45	10.605%	$10.4522	$10.45	$10.45	$10.50
Purchase #7	$85.96	10.453%	$94.9454	$94.95	$94.95	$94.90
7 purchase totals =	$779.74		$858.8404	$858.85	$858.85	$858.90