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	$197.87	13.830%	$225.2354	$225.24	$225.25	$225.20
Purchase #2	$111.81	7.874%	$120.6139	$120.61	$120.60	$120.60
Purchase #3	$96.36	3.298%	$99.538	$99.54	$99.55	$99.50
Purchase #4	$105.97	5.485%	$111.7825	$111.78	$111.80	$111.80
Purchase #5	$176.56	3.628%	$182.9656	$182.97	$182.95	$183.00
Purchase #6	$41.67	8.241%	$45.104	$45.10	$45.10	$45.10
Purchase #7	$79.54	13.716%	$90.4497	$90.45	$90.45	$90.40
7 purchase totals =	$809.78		$875.6891	$875.69	$875.70	$875.60