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	$81.79	4.682%	$85.6194	$85.62	$85.60	$85.60
Purchase #2	$140.39	13.123%	$158.8134	$158.81	$158.80	$158.80
Purchase #3	$38.88	12.300%	$43.6622	$43.66	$43.65	$43.70
Purchase #4	$68.74	5.264%	$72.3585	$72.36	$72.35	$72.40
Purchase #5	$128.58	8.394%	$139.373	$139.37	$139.35	$139.40
Purchase #6	$216.53	10.519%	$239.3068	$239.31	$239.30	$239.30
Purchase #7	$81.99	5.810%	$86.7536	$86.75	$86.75	$86.80
7 purchase totals =	$756.90		$825.8869	$825.88	$825.80	$826.00