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	$121.88	11.858%	$136.3325	$136.33	$136.35	$136.30
Purchase #2	$153.59	13.231%	$173.9115	$173.91	$173.90	$173.90
Purchase #3	$90.98	5.712%	$96.1768	$96.18	$96.20	$96.20
Purchase #4	$76.79	7.536%	$82.5769	$82.58	$82.60	$82.60
Purchase #5	$58.75	3.770%	$60.9649	$60.96	$60.95	$61.00
Purchase #6	$32.71	13.803%	$37.225	$37.23	$37.25	$37.20
Purchase #7	$203.72	6.605%	$217.1757	$217.18	$217.20	$217.20
7 purchase totals =	$738.42		$804.3633	$804.37	$804.45	$804.40