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	$40.96	4.641%	$42.861	$42.86	$42.85	$42.90
Purchase #2	$159.35	10.618%	$176.2698	$176.27	$176.25	$176.30
Purchase #3	$145.50	10.351%	$160.5607	$160.56	$160.55	$160.60
Purchase #4	$19.68	5.609%	$20.7839	$20.78	$20.80	$20.80
Purchase #5	$195.91	11.466%	$218.373	$218.37	$218.35	$218.40
Purchase #6	$170.25	10.492%	$188.1126	$188.11	$188.10	$188.10
Purchase #7	$66.41	12.189%	$74.5047	$74.50	$74.50	$74.50
7 purchase totals =	$798.06		$881.4657	$881.45	$881.40	$881.60