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	$35.35	13.509%	$40.1254	$40.13	$40.15	$40.10
Purchase #2	$102.31	9.706%	$112.2402	$112.24	$112.25	$112.20
Purchase #3	$11.93	9.825%	$13.1021	$13.10	$13.10	$13.10
Purchase #4	$148.75	7.165%	$159.4079	$159.41	$159.40	$159.40
Purchase #5	$158.29	4.568%	$165.5207	$165.52	$165.50	$165.50
Purchase #6	$73.93	9.396%	$80.8765	$80.88	$80.90	$80.90
Purchase #7	$64.51	11.456%	$71.9003	$71.90	$71.90	$71.90
7 purchase totals =	$595.07		$643.1731	$643.18	$643.20	$643.10