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	$238.90	4.533%	$249.7293	$249.73	$249.75	$249.70
Purchase #2	$150.89	13.434%	$171.1606	$171.16	$171.15	$171.20
Purchase #3	$15.45	9.465%	$16.9123	$16.91	$16.90	$16.90
Purchase #4	$241.63	5.849%	$255.7629	$255.76	$255.75	$255.80
Purchase #5	$99.74	11.526%	$111.236	$111.24	$111.25	$111.20
Purchase #6	$135.78	6.268%	$144.2907	$144.29	$144.30	$144.30
Purchase #7	$177.97	3.286%	$183.8181	$183.82	$183.80	$183.80
7 purchase totals =	$1,060.36		$1,132.9099	$1,132.91	$1,132.90	$1,132.90