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	$100.53	4.321%	$104.8739	$104.87	$104.85	$104.90
Purchase #2	$146.43	8.143%	$158.3538	$158.35	$158.35	$158.40
Purchase #3	$221.94	8.388%	$240.5563	$240.56	$240.55	$240.60
Purchase #4	$65.33	4.577%	$68.3202	$68.32	$68.30	$68.30
Purchase #5	$50.53	10.372%	$55.771	$55.77	$55.75	$55.80
Purchase #6	$42.49	7.682%	$45.7541	$45.75	$45.75	$45.80
Purchase #7	$159.64	12.182%	$179.0873	$179.09	$179.10	$179.10
7 purchase totals =	$786.89		$852.7166	$852.71	$852.65	$852.90