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	$171.63	4.520%	$179.3877	$179.39	$179.40	$179.40
Purchase #2	$199.77	3.566%	$206.8938	$206.89	$206.90	$206.90
Purchase #3	$247.66	13.522%	$281.1486	$281.15	$281.15	$281.10
Purchase #4	$63.98	9.435%	$70.0165	$70.02	$70.00	$70.00
Purchase #5	$58.66	13.763%	$66.7334	$66.73	$66.75	$66.70
Purchase #6	$75.29	4.392%	$78.5967	$78.60	$78.60	$78.60
Purchase #7	$123.39	11.283%	$137.3121	$137.31	$137.30	$137.30
7 purchase totals =	$940.38		$1,020.0888	$1,020.09	$1,020.10	$1,020.00