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	$59.82	7.463%	$64.2844	$64.28	$64.30	$64.30
Purchase #2	$110.76	8.600%	$120.2854	$120.29	$120.30	$120.30
Purchase #3	$90.77	9.600%	$99.4839	$99.48	$99.50	$99.50
Purchase #4	$44.56	11.712%	$49.7789	$49.78	$49.80	$49.80
Purchase #5	$37.31	4.439%	$38.9662	$38.97	$38.95	$39.00
Purchase #6	$62.78	5.481%	$66.221	$66.22	$66.20	$66.20
Purchase #7	$137.57	13.488%	$156.1254	$156.13	$156.15	$156.10
7 purchase totals =	$543.57		$595.1452	$595.15	$595.20	$595.20