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	$171.68	11.703%	$191.7717	$191.77	$191.75	$191.80
Purchase #2	$226.71	13.547%	$257.4224	$257.42	$257.40	$257.40
Purchase #3	$70.89	10.824%	$78.5631	$78.56	$78.55	$78.60
Purchase #4	$90.27	8.473%	$97.9186	$97.92	$97.90	$97.90
Purchase #5	$76.75	9.532%	$84.0658	$84.07	$84.05	$84.10
Purchase #6	$82.30	10.247%	$90.7333	$90.73	$90.75	$90.70
Purchase #7	$83.37	9.745%	$91.4944	$91.49	$91.50	$91.50
7 purchase totals =	$801.97		$891.9693	$891.96	$891.90	$892.00