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	$238.93	3.378%	$247.0011	$247.00	$247.00	$247.00
Purchase #2	$74.90	5.269%	$78.8465	$78.85	$78.85	$78.80
Purchase #3	$141.64	3.151%	$146.1031	$146.10	$146.10	$146.10
Purchase #4	$31.34	11.304%	$34.8827	$34.88	$34.90	$34.90
Purchase #5	$75.51	3.376%	$78.0592	$78.06	$78.05	$78.10
Purchase #6	$250.30	11.746%	$279.7002	$279.70	$279.70	$279.70
Purchase #7	$83.86	9.722%	$92.0129	$92.01	$92.00	$92.00
7 purchase totals =	$896.48		$956.6057	$956.60	$956.60	$956.60