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	$79.32	12.302%	$89.0779	$89.08	$89.10	$89.10
Purchase #2	$128.43	12.574%	$144.5788	$144.58	$144.60	$144.60
Purchase #3	$78.90	8.571%	$85.6625	$85.66	$85.65	$85.70
Purchase #4	$134.39	10.163%	$148.0481	$148.05	$148.05	$148.00
Purchase #5	$40.42	13.362%	$45.8209	$45.82	$45.80	$45.80
Purchase #6	$38.55	4.380%	$40.2385	$40.24	$40.25	$40.20
Purchase #7	$210.96	6.861%	$225.434	$225.43	$225.45	$225.40
7 purchase totals =	$710.97		$778.8607	$778.86	$778.90	$778.80