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	$40.29	4.441%	$42.0793	$42.08	$42.10	$42.10
Purchase #2	$139.73	5.793%	$147.8246	$147.82	$147.80	$147.80
Purchase #3	$165.89	10.544%	$183.3814	$183.38	$183.40	$183.40
Purchase #4	$56.81	8.136%	$61.4321	$61.43	$61.45	$61.40
Purchase #5	$151.55	5.760%	$160.2793	$160.28	$160.30	$160.30
Purchase #6	$15.98	5.347%	$16.8345	$16.83	$16.85	$16.80
Purchase #7	$101.64	10.763%	$112.5795	$112.58	$112.60	$112.60
7 purchase totals =	$671.89		$724.4107	$724.40	$724.50	$724.40