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	$99.25	5.246%	$104.4567	$104.46	$104.45	$104.50
Purchase #2	$40.94	4.801%	$42.9055	$42.91	$42.90	$42.90
Purchase #3	$130.27	11.261%	$144.9397	$144.94	$144.95	$144.90
Purchase #4	$27.25	12.323%	$30.608	$30.61	$30.60	$30.60
Purchase #5	$214.27	7.626%	$230.6102	$230.61	$230.60	$230.60
Purchase #6	$110.31	8.630%	$119.8298	$119.83	$119.85	$119.80
Purchase #7	$141.49	3.201%	$146.0191	$146.02	$146.00	$146.00
7 purchase totals =	$763.78		$819.3690	$819.38	$819.35	$819.30