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	$123.26	11.488%	$137.4201	$137.42	$137.40	$137.40
Purchase #2	$244.73	11.665%	$273.2778	$273.28	$273.30	$273.30
Purchase #3	$41.31	9.519%	$45.2423	$45.24	$45.25	$45.20
Purchase #4	$18.99	13.819%	$21.6142	$21.61	$21.60	$21.60
Purchase #5	$47.42	6.368%	$50.4397	$50.44	$50.45	$50.40
Purchase #6	$157.37	11.211%	$175.0128	$175.01	$175.00	$175.00
Purchase #7	$230.56	3.295%	$238.157	$238.16	$238.15	$238.20
7 purchase totals =	$863.64		$941.1639	$941.16	$941.15	$941.10