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	$236.49	9.446%	$258.8288	$258.83	$258.85	$258.80
Purchase #2	$188.40	10.340%	$207.8806	$207.88	$207.90	$207.90
Purchase #3	$31.86	5.784%	$33.7028	$33.70	$33.70	$33.70
Purchase #4	$92.98	11.796%	$103.9479	$103.95	$103.95	$103.90
Purchase #5	$59.92	9.239%	$65.456	$65.46	$65.45	$65.50
Purchase #6	$169.59	9.422%	$185.5688	$185.57	$185.55	$185.60
Purchase #7	$164.45	13.826%	$187.1869	$187.19	$187.20	$187.20
7 purchase totals =	$943.69		$1,042.5718	$1,042.58	$1,042.60	$1,042.60