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	$172.76	6.325%	$183.6871	$183.69	$183.70	$183.70
Purchase #2	$79.75	4.649%	$83.4576	$83.46	$83.45	$83.50
Purchase #3	$18.45	8.640%	$20.0441	$20.04	$20.05	$20.00
Purchase #4	$130.56	13.727%	$148.482	$148.48	$148.50	$148.50
Purchase #5	$152.35	10.604%	$168.5052	$168.51	$168.50	$168.50
Purchase #6	$165.68	3.497%	$171.4738	$171.47	$171.45	$171.50
Purchase #7	$57.87	9.151%	$63.1657	$63.17	$63.15	$63.20
7 purchase totals =	$777.42		$838.8155	$838.82	$838.80	$838.90