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	$11.57	10.156%	$12.745	$12.75	$12.75	$12.70
Purchase #2	$112.56	9.428%	$123.1722	$123.17	$123.15	$123.20
Purchase #3	$119.65	11.694%	$133.6419	$133.64	$133.65	$133.60
Purchase #4	$172.28	3.250%	$177.8791	$177.88	$177.90	$177.90
Purchase #5	$195.79	13.476%	$222.1747	$222.17	$222.15	$222.20
Purchase #6	$19.50	6.196%	$20.7082	$20.71	$20.70	$20.70
Purchase #7	$31.77	10.671%	$35.1602	$35.16	$35.15	$35.20
7 purchase totals =	$663.12		$725.4813	$725.48	$725.45	$725.50