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	$123.94	4.533%	$129.5582	$129.56	$129.55	$129.60
Purchase #2	$28.86	8.492%	$31.3108	$31.31	$31.30	$31.30
Purchase #3	$172.60	13.806%	$196.4292	$196.43	$196.45	$196.40
Purchase #4	$110.41	10.509%	$122.013	$122.01	$122.00	$122.00
Purchase #5	$234.27	12.614%	$263.8208	$263.82	$263.80	$263.80
Purchase #6	$228.49	6.321%	$242.9329	$242.93	$242.95	$242.90
Purchase #7	$165.48	4.420%	$172.7942	$172.79	$172.80	$172.80
7 purchase totals =	$1,064.05		$1,158.8591	$1,158.85	$1,158.85	$1,158.80