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	$78.48	6.408%	$83.509	$83.51	$83.50	$83.50
Purchase #2	$77.58	4.759%	$81.272	$81.27	$81.25	$81.30
Purchase #3	$175.45	11.804%	$196.1601	$196.16	$196.15	$196.20
Purchase #4	$127.32	9.658%	$139.6166	$139.62	$139.60	$139.60
Purchase #5	$185.47	13.532%	$210.5678	$210.57	$210.55	$210.60
Purchase #6	$15.84	4.750%	$16.5924	$16.59	$16.60	$16.60
Purchase #7	$82.59	10.138%	$90.963	$90.96	$90.95	$91.00
7 purchase totals =	$742.73		$818.6809	$818.68	$818.60	$818.80