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	$93.51	9.803%	$102.6768	$102.68	$102.70	$102.70
Purchase #2	$54.33	13.833%	$61.8455	$61.85	$61.85	$61.80
Purchase #3	$18.81	11.785%	$21.0268	$21.03	$21.05	$21.00
Purchase #4	$176.87	4.740%	$185.2536	$185.25	$185.25	$185.30
Purchase #5	$112.41	9.280%	$122.8416	$122.84	$122.85	$122.80
Purchase #6	$6.53	8.262%	$7.0695	$7.07	$7.05	$7.10
Purchase #7	$100.68	10.624%	$111.3762	$111.38	$111.40	$111.40
7 purchase totals =	$563.14		$612.0900	$612.10	$612.15	$612.10