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	$74.95	11.854%	$83.8346	$83.83	$83.85	$83.80
Purchase #2	$213.60	9.299%	$233.4627	$233.46	$233.45	$233.50
Purchase #3	$71.87	4.797%	$75.3176	$75.32	$75.30	$75.30
Purchase #4	$41.94	10.663%	$46.4121	$46.41	$46.40	$46.40
Purchase #5	$130.52	7.740%	$140.6222	$140.62	$140.60	$140.60
Purchase #6	$72.59	13.773%	$82.5878	$82.59	$82.60	$82.60
Purchase #7	$138.78	4.255%	$144.6851	$144.69	$144.70	$144.70
7 purchase totals =	$744.25		$806.9221	$806.92	$806.90	$806.90