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	$158.54	7.238%	$170.0151	$170.02	$170.00	$170.00
Purchase #2	$34.59	5.239%	$36.4022	$36.40	$36.40	$36.40
Purchase #3	$145.86	8.581%	$158.3762	$158.38	$158.40	$158.40
Purchase #4	$36.37	4.692%	$38.0765	$38.08	$38.10	$38.10
Purchase #5	$140.72	6.813%	$150.3073	$150.31	$150.30	$150.30
Purchase #6	$50.36	13.112%	$56.9632	$56.96	$56.95	$57.00
Purchase #7	$96.45	3.311%	$99.6435	$99.64	$99.65	$99.60
7 purchase totals =	$662.89		$709.7840	$709.79	$709.80	$709.80