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	$76.61	7.406%	$82.2837	$82.28	$82.30	$82.30
Purchase #2	$40.60	6.556%	$43.2617	$43.26	$43.25	$43.30
Purchase #3	$58.63	5.507%	$61.8588	$61.86	$61.85	$61.90
Purchase #4	$155.61	11.680%	$173.7852	$173.79	$173.80	$173.80
Purchase #5	$187.92	10.587%	$207.8151	$207.82	$207.80	$207.80
Purchase #6	$83.82	10.188%	$92.3596	$92.36	$92.35	$92.40
Purchase #7	$161.26	6.726%	$172.1063	$172.11	$172.10	$172.10
7 purchase totals =	$764.45		$833.4704	$833.48	$833.45	$833.60