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	$9.28	11.518%	$10.3489	$10.35	$10.35	$10.30
Purchase #2	$31.38	4.834%	$32.8969	$32.90	$32.90	$32.90
Purchase #3	$113.66	12.501%	$127.8686	$127.87	$127.85	$127.90
Purchase #4	$59.80	12.412%	$67.2224	$67.22	$67.20	$67.20
Purchase #5	$38.43	6.173%	$40.8023	$40.80	$40.80	$40.80
Purchase #6	$34.92	10.225%	$38.4906	$38.49	$38.50	$38.50
Purchase #7	$32.36	9.595%	$35.4649	$35.46	$35.45	$35.50
7 purchase totals =	$319.83		$353.0946	$353.09	$353.05	$353.10