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	$79.69	7.236%	$85.4564	$85.46	$85.45	$85.50
Purchase #2	$230.75	6.113%	$244.8557	$244.86	$244.85	$244.90
Purchase #3	$40.25	3.201%	$41.5384	$41.54	$41.55	$41.50
Purchase #4	$60.89	9.169%	$66.473	$66.47	$66.45	$66.50
Purchase #5	$70.30	3.827%	$72.9904	$72.99	$73.00	$73.00
Purchase #6	$74.96	7.805%	$80.8106	$80.81	$80.80	$80.80
Purchase #7	$65.81	7.380%	$70.6668	$70.67	$70.65	$70.70
7 purchase totals =	$622.65		$662.7913	$662.80	$662.75	$662.90