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	$42.92	3.579%	$44.4561	$44.46	$44.45	$44.50
Purchase #2	$232.44	9.659%	$254.8914	$254.89	$254.90	$254.90
Purchase #3	$132.32	5.530%	$139.6373	$139.64	$139.65	$139.60
Purchase #4	$229.59	12.665%	$258.6676	$258.67	$258.65	$258.70
Purchase #5	$123.91	5.299%	$130.476	$130.48	$130.50	$130.50
Purchase #6	$45.33	8.631%	$49.2424	$49.24	$49.25	$49.20
Purchase #7	$99.97	3.163%	$103.1321	$103.13	$103.15	$103.10
7 purchase totals =	$906.48		$980.5029	$980.51	$980.55	$980.50