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	$74.55	12.468%	$83.8449	$83.84	$83.85	$83.80
Purchase #2	$84.66	5.842%	$89.6058	$89.61	$89.60	$89.60
Purchase #3	$133.52	9.630%	$146.378	$146.38	$146.40	$146.40
Purchase #4	$166.60	12.692%	$187.7449	$187.74	$187.75	$187.70
Purchase #5	$172.34	7.805%	$185.7911	$185.79	$185.80	$185.80
Purchase #6	$126.32	13.342%	$143.1736	$143.17	$143.15	$143.20
Purchase #7	$232.56	8.732%	$252.8671	$252.87	$252.85	$252.90
7 purchase totals =	$990.55		$1,089.4054	$1,089.40	$1,089.40	$1,089.40