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	$157.44	5.652%	$166.3385	$166.34	$166.35	$166.30
Purchase #2	$138.83	10.179%	$152.9615	$152.96	$152.95	$153.00
Purchase #3	$219.65	12.231%	$246.5154	$246.52	$246.50	$246.50
Purchase #4	$19.48	4.237%	$20.3054	$20.31	$20.30	$20.30
Purchase #5	$52.49	9.703%	$57.5831	$57.58	$57.60	$57.60
Purchase #6	$78.54	13.331%	$89.0102	$89.01	$89.00	$89.00
Purchase #7	$92.81	8.405%	$100.6107	$100.61	$100.60	$100.60
7 purchase totals =	$759.24		$833.3248	$833.33	$833.30	$833.30