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	$158.56	7.580%	$170.5788	$170.58	$170.60	$170.60
Purchase #2	$172.52	3.511%	$178.5772	$178.58	$178.60	$178.60
Purchase #3	$219.59	13.128%	$248.4178	$248.42	$248.40	$248.40
Purchase #4	$188.99	6.294%	$200.885	$200.89	$200.90	$200.90
Purchase #5	$79.37	13.599%	$90.1635	$90.16	$90.15	$90.20
Purchase #6	$128.29	7.534%	$137.9554	$137.96	$137.95	$138.00
Purchase #7	$116.93	12.674%	$131.7497	$131.75	$131.75	$131.70
7 purchase totals =	$1,064.25		$1,158.3274	$1,158.34	$1,158.35	$1,158.40