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	$87.90	11.627%	$98.1201	$98.12	$98.10	$98.10
Purchase #2	$32.41	7.627%	$34.8819	$34.88	$34.90	$34.90
Purchase #3	$250.62	12.644%	$282.3084	$282.31	$282.30	$282.30
Purchase #4	$212.98	3.303%	$220.0147	$220.01	$220.00	$220.00
Purchase #5	$118.27	10.436%	$130.6127	$130.61	$130.60	$130.60
Purchase #6	$81.89	9.727%	$89.8554	$89.86	$89.85	$89.90
Purchase #7	$217.86	13.396%	$247.0445	$247.04	$247.05	$247.00
7 purchase totals =	$1,001.93		$1,102.8377	$1,102.83	$1,102.80	$1,102.80