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	$6.60	10.293%	$7.2793	$7.28	$7.30	$7.30
Purchase #2	$37.46	13.358%	$42.4639	$42.46	$42.45	$42.50
Purchase #3	$123.52	8.704%	$134.2712	$134.27	$134.25	$134.30
Purchase #4	$186.60	5.254%	$196.404	$196.40	$196.40	$196.40
Purchase #5	$19.43	7.232%	$20.8352	$20.84	$20.85	$20.80
Purchase #6	$195.61	5.190%	$205.7622	$205.76	$205.75	$205.80
Purchase #7	$12.78	3.304%	$13.2023	$13.20	$13.20	$13.20
7 purchase totals =	$582.00		$620.2181	$620.21	$620.20	$620.30