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	$161.44	6.677%	$172.2193	$172.22	$172.20	$172.20
Purchase #2	$131.28	8.559%	$142.5163	$142.52	$142.50	$142.50
Purchase #3	$178.62	12.309%	$200.6063	$200.61	$200.60	$200.60
Purchase #4	$155.95	10.156%	$171.7883	$171.79	$171.80	$171.80
Purchase #5	$187.73	12.350%	$210.9147	$210.91	$210.90	$210.90
Purchase #6	$220.28	3.421%	$227.8158	$227.82	$227.80	$227.80
Purchase #7	$54.72	7.405%	$58.772	$58.77	$58.75	$58.80
7 purchase totals =	$1,090.02		$1,184.6327	$1,184.64	$1,184.55	$1,184.60