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	$247.77	11.257%	$275.6615	$275.66	$275.65	$275.70
Purchase #2	$39.56	5.791%	$41.8509	$41.85	$41.85	$41.90
Purchase #3	$55.60	4.262%	$57.9697	$57.97	$57.95	$58.00
Purchase #4	$67.66	7.579%	$72.788	$72.79	$72.80	$72.80
Purchase #5	$14.94	7.414%	$16.0477	$16.05	$16.05	$16.00
Purchase #6	$12.40	6.704%	$13.2313	$13.23	$13.25	$13.20
Purchase #7	$179.39	5.172%	$188.6681	$188.67	$188.65	$188.70
7 purchase totals =	$617.32		$666.2172	$666.22	$666.20	$666.30