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	$143.42	12.802%	$161.7806	$161.78	$161.80	$161.80
Purchase #2	$46.56	8.650%	$50.5874	$50.59	$50.60	$50.60
Purchase #3	$111.51	5.456%	$117.594	$117.59	$117.60	$117.60
Purchase #4	$39.30	9.147%	$42.8948	$42.89	$42.90	$42.90
Purchase #5	$8.25	12.148%	$9.2522	$9.25	$9.25	$9.30
Purchase #6	$91.28	9.139%	$99.6221	$99.62	$99.60	$99.60
Purchase #7	$6.84	8.628%	$7.4302	$7.43	$7.45	$7.40
7 purchase totals =	$447.16		$489.1613	$489.15	$489.20	$489.20