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	$229.86	4.802%	$240.8979	$240.90	$240.90	$240.90
Purchase #2	$180.95	6.422%	$192.5706	$192.57	$192.55	$192.60
Purchase #3	$131.48	5.262%	$138.3985	$138.40	$138.40	$138.40
Purchase #4	$145.89	7.461%	$156.7749	$156.77	$156.75	$156.80
Purchase #5	$140.56	8.385%	$152.346	$152.35	$152.35	$152.30
Purchase #6	$26.38	7.366%	$28.3232	$28.32	$28.30	$28.30
Purchase #7	$19.78	4.149%	$20.6007	$20.60	$20.60	$20.60
7 purchase totals =	$874.90		$929.9118	$929.91	$929.85	$929.90