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	$29.99	4.205%	$31.2511	$31.25	$31.25	$31.30
Purchase #2	$51.49	3.518%	$53.3014	$53.30	$53.30	$53.30
Purchase #3	$94.60	11.248%	$105.2406	$105.24	$105.25	$105.20
Purchase #4	$104.50	13.273%	$118.3703	$118.37	$118.35	$118.40
Purchase #5	$46.29	9.301%	$50.5954	$50.60	$50.60	$50.60
Purchase #6	$181.94	11.171%	$202.2645	$202.26	$202.25	$202.30
Purchase #7	$96.61	5.465%	$101.8897	$101.89	$101.90	$101.90
7 purchase totals =	$605.42		$662.9130	$662.91	$662.90	$663.00