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	$46.41	10.487%	$51.277	$51.28	$51.30	$51.30
Purchase #2	$157.85	11.677%	$176.2821	$176.28	$176.30	$176.30
Purchase #3	$127.44	8.292%	$138.0073	$138.01	$138.00	$138.00
Purchase #4	$127.71	12.369%	$143.5064	$143.51	$143.50	$143.50
Purchase #5	$77.43	4.750%	$81.1079	$81.11	$81.10	$81.10
Purchase #6	$248.77	10.794%	$275.6222	$275.62	$275.60	$275.60
Purchase #7	$83.93	6.740%	$89.5869	$89.59	$89.60	$89.60
7 purchase totals =	$869.54		$955.3898	$955.40	$955.40	$955.40