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	$93.95	6.106%	$99.6866	$99.69	$99.70	$99.70
Purchase #2	$35.80	9.591%	$39.2336	$39.23	$39.25	$39.20
Purchase #3	$166.51	4.822%	$174.5391	$174.54	$174.55	$174.50
Purchase #4	$24.54	12.792%	$27.6792	$27.68	$27.70	$27.70
Purchase #5	$140.39	9.106%	$153.1739	$153.17	$153.15	$153.20
Purchase #6	$163.62	5.361%	$172.3917	$172.39	$172.40	$172.40
Purchase #7	$153.59	7.166%	$164.5963	$164.60	$164.60	$164.60
7 purchase totals =	$778.40		$831.3004	$831.30	$831.35	$831.30