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	$208.35	7.264%	$223.4845	$223.48	$223.50	$223.50
Purchase #2	$179.96	8.850%	$195.8865	$195.89	$195.90	$195.90
Purchase #3	$65.88	7.262%	$70.6642	$70.66	$70.65	$70.70
Purchase #4	$81.45	5.558%	$85.977	$85.98	$86.00	$86.00
Purchase #5	$68.45	11.492%	$76.3163	$76.32	$76.30	$76.30
Purchase #6	$35.95	4.553%	$37.5868	$37.59	$37.60	$37.60
Purchase #7	$137.26	10.677%	$151.9153	$151.92	$151.90	$151.90
7 purchase totals =	$777.30		$841.8306	$841.84	$841.85	$841.90