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	$171.56	4.707%	$179.6353	$179.64	$179.65	$179.60
Purchase #2	$103.80	5.773%	$109.7924	$109.79	$109.80	$109.80
Purchase #3	$33.73	12.800%	$38.0474	$38.05	$38.05	$38.00
Purchase #4	$52.40	12.712%	$59.0611	$59.06	$59.05	$59.10
Purchase #5	$217.50	5.625%	$229.7344	$229.73	$229.75	$229.70
Purchase #6	$49.95	12.457%	$56.1723	$56.17	$56.15	$56.20
Purchase #7	$128.61	10.125%	$141.6318	$141.63	$141.65	$141.60
7 purchase totals =	$757.55		$814.0747	$814.07	$814.10	$814.00