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	$87.93	3.753%	$91.23	$91.23	$91.25	$91.20
Purchase #2	$41.90	8.115%	$45.3002	$45.30	$45.30	$45.30
Purchase #3	$210.85	13.286%	$238.8635	$238.86	$238.85	$238.90
Purchase #4	$142.31	4.257%	$148.3681	$148.37	$148.35	$148.40
Purchase #5	$128.89	3.563%	$133.4824	$133.48	$133.50	$133.50
Purchase #6	$128.61	13.514%	$145.9904	$145.99	$146.00	$146.00
Purchase #7	$102.34	6.858%	$109.3585	$109.36	$109.35	$109.40
7 purchase totals =	$842.83		$912.5931	$912.59	$912.60	$912.70