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	$89.62	12.693%	$100.9955	$101.00	$101.00	$101.00
Purchase #2	$74.76	5.305%	$78.726	$78.73	$78.75	$78.70
Purchase #3	$64.92	8.132%	$70.1993	$70.20	$70.20	$70.20
Purchase #4	$12.47	4.139%	$12.9861	$12.99	$13.00	$13.00
Purchase #5	$35.47	6.175%	$37.6603	$37.66	$37.65	$37.70
Purchase #6	$56.53	5.136%	$59.4334	$59.43	$59.45	$59.40
Purchase #7	$212.35	6.128%	$225.3628	$225.36	$225.35	$225.40
7 purchase totals =	$546.12		$585.3634	$585.37	$585.40	$585.40