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	$36.47	5.524%	$38.4846	$38.48	$38.50	$38.50
Purchase #2	$14.82	11.188%	$16.4781	$16.48	$16.50	$16.50
Purchase #3	$7.82	6.363%	$8.3176	$8.32	$8.30	$8.30
Purchase #4	$127.73	13.356%	$144.7896	$144.79	$144.80	$144.80
Purchase #5	$99.32	12.666%	$111.8999	$111.90	$111.90	$111.90
Purchase #6	$167.29	10.576%	$184.9826	$184.98	$185.00	$185.00
Purchase #7	$146.60	4.240%	$152.8158	$152.82	$152.80	$152.80
7 purchase totals =	$600.05		$657.7682	$657.77	$657.80	$657.80