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	$6.74	13.491%	$7.6493	$7.65	$7.65	$7.60
Purchase #2	$225.88	6.609%	$240.8084	$240.81	$240.80	$240.80
Purchase #3	$183.80	11.523%	$204.9793	$204.98	$205.00	$205.00
Purchase #4	$67.83	4.750%	$71.0519	$71.05	$71.05	$71.10
Purchase #5	$14.46	7.194%	$15.5003	$15.50	$15.50	$15.50
Purchase #6	$13.82	13.543%	$15.6916	$15.69	$15.70	$15.70
Purchase #7	$64.29	13.209%	$72.7821	$72.78	$72.80	$72.80
7 purchase totals =	$576.82		$628.4629	$628.46	$628.50	$628.50