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	$224.97	8.707%	$244.5581	$244.56	$244.55	$244.60
Purchase #2	$151.79	11.223%	$168.8254	$168.83	$168.85	$168.80
Purchase #3	$20.63	9.314%	$22.5515	$22.55	$22.55	$22.60
Purchase #4	$80.95	10.527%	$89.4716	$89.47	$89.45	$89.50
Purchase #5	$15.78	9.451%	$17.2714	$17.27	$17.25	$17.30
Purchase #6	$46.89	5.185%	$49.3212	$49.32	$49.30	$49.30
Purchase #7	$69.91	6.304%	$74.3171	$74.32	$74.30	$74.30
7 purchase totals =	$610.92		$666.3163	$666.32	$666.25	$666.40