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	$7.36	6.224%	$7.8181	$7.82	$7.80	$7.80
Purchase #2	$241.66	5.564%	$255.106	$255.11	$255.10	$255.10
Purchase #3	$158.83	4.357%	$165.7502	$165.75	$165.75	$165.80
Purchase #4	$82.95	11.658%	$92.6203	$92.62	$92.60	$92.60
Purchase #5	$26.80	7.619%	$28.8419	$28.84	$28.85	$28.80
Purchase #6	$54.28	3.479%	$56.1684	$56.17	$56.15	$56.20
Purchase #7	$95.39	9.666%	$104.6104	$104.61	$104.60	$104.60
7 purchase totals =	$667.27		$710.9153	$710.92	$710.85	$710.90