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	$99.87	11.310%	$111.1653	$111.17	$111.15	$111.20
Purchase #2	$198.40	3.411%	$205.1674	$205.17	$205.15	$205.20
Purchase #3	$18.68	10.235%	$20.5919	$20.59	$20.60	$20.60
Purchase #4	$25.88	6.311%	$27.5133	$27.51	$27.50	$27.50
Purchase #5	$19.46	3.357%	$20.1133	$20.11	$20.10	$20.10
Purchase #6	$55.86	12.433%	$62.8051	$62.81	$62.80	$62.80
Purchase #7	$39.58	8.141%	$42.8022	$42.80	$42.80	$42.80
7 purchase totals =	$457.73		$490.1585	$490.16	$490.10	$490.20