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	$210.52	13.130%	$238.1613	$238.16	$238.15	$238.20
Purchase #2	$58.29	3.173%	$60.1395	$60.14	$60.15	$60.10
Purchase #3	$83.92	5.482%	$88.5205	$88.52	$88.50	$88.50
Purchase #4	$144.48	13.864%	$164.5107	$164.51	$164.50	$164.50
Purchase #5	$120.40	11.612%	$134.3808	$134.38	$134.40	$134.40
Purchase #6	$78.45	10.281%	$86.5154	$86.52	$86.50	$86.50
Purchase #7	$25.28	13.162%	$28.6074	$28.61	$28.60	$28.60
7 purchase totals =	$721.34		$800.8356	$800.84	$800.80	$800.80