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	$230.58	12.344%	$259.0428	$259.04	$259.05	$259.00
Purchase #2	$155.34	8.436%	$168.4445	$168.44	$168.45	$168.40
Purchase #3	$146.26	13.813%	$166.4629	$166.46	$166.45	$166.50
Purchase #4	$111.25	10.849%	$123.3195	$123.32	$123.30	$123.30
Purchase #5	$27.80	8.395%	$30.1338	$30.13	$30.15	$30.10
Purchase #6	$55.77	10.757%	$61.7692	$61.77	$61.75	$61.80
Purchase #7	$34.61	12.118%	$38.804	$38.80	$38.80	$38.80
7 purchase totals =	$761.61		$847.9767	$847.96	$847.95	$847.90