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	$49.42	6.497%	$52.6308	$52.63	$52.65	$52.60
Purchase #2	$130.46	10.636%	$144.3357	$144.34	$144.35	$144.30
Purchase #3	$152.31	7.361%	$163.5215	$163.52	$163.50	$163.50
Purchase #4	$234.56	12.474%	$263.819	$263.82	$263.80	$263.80
Purchase #5	$175.59	5.308%	$184.9103	$184.91	$184.90	$184.90
Purchase #6	$90.63	5.177%	$95.3219	$95.32	$95.30	$95.30
Purchase #7	$70.47	11.333%	$78.4564	$78.46	$78.45	$78.50
7 purchase totals =	$903.44		$982.9956	$983.00	$982.95	$982.90