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	$138.29	8.162%	$149.5772	$149.58	$149.60	$149.60
Purchase #2	$125.38	13.784%	$142.6624	$142.66	$142.65	$142.70
Purchase #3	$78.39	12.846%	$88.46	$88.46	$88.45	$88.50
Purchase #4	$55.34	7.665%	$59.5818	$59.58	$59.60	$59.60
Purchase #5	$32.46	7.225%	$34.8052	$34.81	$34.80	$34.80
Purchase #6	$129.45	6.397%	$137.7309	$137.73	$137.75	$137.70
Purchase #7	$174.28	8.396%	$188.9125	$188.91	$188.90	$188.90
7 purchase totals =	$733.59		$801.7300	$801.73	$801.75	$801.80