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	$56.28	6.114%	$59.721	$59.72	$59.70	$59.70
Purchase #2	$92.80	12.436%	$104.3406	$104.34	$104.35	$104.30
Purchase #3	$181.82	13.754%	$206.8275	$206.83	$206.85	$206.80
Purchase #4	$231.89	9.579%	$254.1027	$254.10	$254.10	$254.10
Purchase #5	$10.25	8.863%	$11.1585	$11.16	$11.15	$11.20
Purchase #6	$82.43	4.234%	$85.9201	$85.92	$85.90	$85.90
Purchase #7	$150.82	11.625%	$168.3528	$168.35	$168.35	$168.40
7 purchase totals =	$806.29		$890.4232	$890.42	$890.40	$890.40