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	$237.37	10.179%	$261.5319	$261.53	$261.55	$261.50
Purchase #2	$33.59	6.724%	$35.8486	$35.85	$35.85	$35.80
Purchase #3	$211.36	5.105%	$222.1499	$222.15	$222.15	$222.10
Purchase #4	$91.83	12.833%	$103.6145	$103.61	$103.60	$103.60
Purchase #5	$97.79	6.366%	$104.0153	$104.02	$104.00	$104.00
Purchase #6	$205.66	13.427%	$233.274	$233.27	$233.25	$233.30
Purchase #7	$37.95	9.861%	$41.6922	$41.69	$41.70	$41.70
7 purchase totals =	$915.55		$1,002.1264	$1,002.12	$1,002.10	$1,002.00