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	$42.56	11.536%	$47.4697	$47.47	$47.45	$47.50
Purchase #2	$111.98	3.221%	$115.5869	$115.59	$115.60	$115.60
Purchase #3	$87.46	12.204%	$98.1336	$98.13	$98.15	$98.10
Purchase #4	$14.44	3.594%	$14.959	$14.96	$14.95	$15.00
Purchase #5	$173.95	9.175%	$189.9099	$189.91	$189.90	$189.90
Purchase #6	$114.27	12.204%	$128.2155	$128.22	$128.20	$128.20
Purchase #7	$69.78	4.336%	$72.8057	$72.81	$72.80	$72.80
7 purchase totals =	$614.44		$667.0803	$667.09	$667.05	$667.10