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	$82.52	3.145%	$85.1153	$85.12	$85.10	$85.10
Purchase #2	$137.52	12.218%	$154.3222	$154.32	$154.30	$154.30
Purchase #3	$87.30	6.232%	$92.7405	$92.74	$92.75	$92.70
Purchase #4	$118.71	13.337%	$134.5424	$134.54	$134.55	$134.50
Purchase #5	$136.39	11.112%	$151.5457	$151.55	$151.55	$151.50
Purchase #6	$30.45	7.647%	$32.7785	$32.78	$32.80	$32.80
Purchase #7	$131.27	11.485%	$146.3464	$146.35	$146.35	$146.30
7 purchase totals =	$724.16		$797.3910	$797.40	$797.40	$797.20