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	$51.48	12.332%	$57.8285	$57.83	$57.85	$57.80
Purchase #2	$28.71	13.284%	$32.5238	$32.52	$32.50	$32.50
Purchase #3	$205.61	5.481%	$216.8795	$216.88	$216.90	$216.90
Purchase #4	$19.77	6.193%	$20.9944	$20.99	$21.00	$21.00
Purchase #5	$178.31	12.150%	$199.9747	$199.97	$199.95	$200.00
Purchase #6	$170.66	10.212%	$188.0878	$188.09	$188.10	$188.10
Purchase #7	$112.44	5.463%	$118.5826	$118.58	$118.60	$118.60
7 purchase totals =	$766.98		$834.8713	$834.86	$834.90	$834.90