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	$204.89	12.475%	$230.45	$230.45	$230.45	$230.50
Purchase #2	$175.91	7.661%	$189.3865	$189.39	$189.40	$189.40
Purchase #3	$51.89	8.380%	$56.2384	$56.24	$56.25	$56.20
Purchase #4	$91.56	10.485%	$101.1601	$101.16	$101.15	$101.20
Purchase #5	$73.81	5.731%	$78.0401	$78.04	$78.05	$78.00
Purchase #6	$75.76	6.405%	$80.6124	$80.61	$80.60	$80.60
Purchase #7	$79.89	8.256%	$86.4857	$86.49	$86.50	$86.50
7 purchase totals =	$753.71		$822.3732	$822.38	$822.40	$822.40