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	$32.60	8.297%	$35.3048	$35.30	$35.30	$35.30
Purchase #2	$58.69	11.151%	$65.2345	$65.23	$65.25	$65.20
Purchase #3	$167.85	12.540%	$188.8984	$188.90	$188.90	$188.90
Purchase #4	$31.64	13.395%	$35.8782	$35.88	$35.90	$35.90
Purchase #5	$130.87	12.230%	$146.8754	$146.88	$146.90	$146.90
Purchase #6	$161.50	12.447%	$181.6019	$181.60	$181.60	$181.60
Purchase #7	$222.56	10.603%	$246.158	$246.16	$246.15	$246.20
7 purchase totals =	$805.71		$899.9512	$899.95	$900.00	$900.00