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	$47.55	3.552%	$49.239	$49.24	$49.25	$49.20
Purchase #2	$105.86	12.825%	$119.4365	$119.44	$119.45	$119.40
Purchase #3	$169.60	12.253%	$190.3811	$190.38	$190.40	$190.40
Purchase #4	$85.86	5.714%	$90.766	$90.77	$90.75	$90.80
Purchase #5	$65.49	3.245%	$67.6152	$67.62	$67.60	$67.60
Purchase #6	$91.35	7.436%	$98.1428	$98.14	$98.15	$98.10
Purchase #7	$41.44	11.370%	$46.1517	$46.15	$46.15	$46.20
7 purchase totals =	$607.15		$661.7323	$661.74	$661.75	$661.70