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	$114.51	8.506%	$124.2502	$124.25	$124.25	$124.30
Purchase #2	$86.66	11.374%	$96.5167	$96.52	$96.50	$96.50
Purchase #3	$192.89	3.707%	$200.0404	$200.04	$200.05	$200.00
Purchase #4	$86.31	7.275%	$92.5891	$92.59	$92.60	$92.60
Purchase #5	$74.28	4.510%	$77.63	$77.63	$77.65	$77.60
Purchase #6	$218.47	8.207%	$236.3998	$236.40	$236.40	$236.40
Purchase #7	$136.72	10.805%	$151.4926	$151.49	$151.50	$151.50
7 purchase totals =	$909.84		$978.9188	$978.92	$978.95	$978.90