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	$130.28	10.407%	$143.8382	$143.84	$143.85	$143.80
Purchase #2	$177.29	7.624%	$190.8066	$190.81	$190.80	$190.80
Purchase #3	$82.45	11.705%	$92.1008	$92.10	$92.10	$92.10
Purchase #4	$123.25	5.294%	$129.7749	$129.77	$129.75	$129.80
Purchase #5	$159.85	7.196%	$171.3528	$171.35	$171.35	$171.40
Purchase #6	$28.51	3.126%	$29.4012	$29.40	$29.40	$29.40
Purchase #7	$76.58	12.155%	$85.8883	$85.89	$85.90	$85.90
7 purchase totals =	$778.21		$843.1628	$843.16	$843.15	$843.20