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	$158.40	8.830%	$172.3867	$172.39	$172.40	$172.40
Purchase #2	$18.52	3.390%	$19.1478	$19.15	$19.15	$19.10
Purchase #3	$90.37	3.799%	$93.8032	$93.80	$93.80	$93.80
Purchase #4	$41.95	12.591%	$47.2319	$47.23	$47.25	$47.20
Purchase #5	$170.41	13.145%	$192.8104	$192.81	$192.80	$192.80
Purchase #6	$177.60	10.606%	$196.4363	$196.44	$196.45	$196.40
Purchase #7	$16.49	12.736%	$18.5902	$18.59	$18.60	$18.60
7 purchase totals =	$673.74		$740.4065	$740.41	$740.45	$740.30