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	$60.98	6.404%	$64.8852	$64.89	$64.90	$64.90
Purchase #2	$40.60	5.573%	$42.8626	$42.86	$42.85	$42.90
Purchase #3	$234.56	4.467%	$245.0378	$245.04	$245.05	$245.00
Purchase #4	$234.66	11.857%	$262.4836	$262.48	$262.50	$262.50
Purchase #5	$212.56	8.534%	$230.6999	$230.70	$230.70	$230.70
Purchase #6	$158.58	4.692%	$166.0206	$166.02	$166.00	$166.00
Purchase #7	$203.38	6.127%	$215.8411	$215.84	$215.85	$215.80
7 purchase totals =	$1,145.32		$1,227.8308	$1,227.83	$1,227.85	$1,227.80