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	$179.82	3.207%	$185.5868	$185.59	$185.60	$185.60
Purchase #2	$133.68	7.464%	$143.6579	$143.66	$143.65	$143.70
Purchase #3	$67.26	4.624%	$70.3701	$70.37	$70.35	$70.40
Purchase #4	$76.41	5.451%	$80.5751	$80.58	$80.60	$80.60
Purchase #5	$127.88	11.692%	$142.8317	$142.83	$142.85	$142.80
Purchase #6	$7.83	13.765%	$8.9078	$8.91	$8.90	$8.90
Purchase #7	$111.35	13.178%	$126.0237	$126.02	$126.00	$126.00
7 purchase totals =	$704.23		$757.9531	$757.96	$757.95	$758.00