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	$143.82	9.456%	$157.4196	$157.42	$157.40	$157.40
Purchase #2	$244.65	9.738%	$268.474	$268.47	$268.45	$268.50
Purchase #3	$87.33	3.338%	$90.2451	$90.25	$90.25	$90.20
Purchase #4	$201.71	11.302%	$224.5073	$224.51	$224.50	$224.50
Purchase #5	$172.77	9.389%	$188.9914	$188.99	$189.00	$189.00
Purchase #6	$245.35	11.478%	$273.5113	$273.51	$273.50	$273.50
Purchase #7	$79.90	12.117%	$89.5815	$89.58	$89.60	$89.60
7 purchase totals =	$1,175.53		$1,292.7302	$1,292.73	$1,292.70	$1,292.70