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	$141.71	10.432%	$156.4932	$156.49	$156.50	$156.50
Purchase #2	$38.92	6.616%	$41.4949	$41.49	$41.50	$41.50
Purchase #3	$65.65	6.606%	$69.9868	$69.99	$70.00	$70.00
Purchase #4	$88.27	12.772%	$99.5438	$99.54	$99.55	$99.50
Purchase #5	$167.53	9.528%	$183.4923	$183.49	$183.50	$183.50
Purchase #6	$75.38	9.197%	$82.3127	$82.31	$82.30	$82.30
Purchase #7	$149.82	13.752%	$170.4232	$170.42	$170.40	$170.40
7 purchase totals =	$727.28		$803.7469	$803.73	$803.75	$803.70