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	$162.25	11.438%	$180.8082	$180.81	$180.80	$180.80
Purchase #2	$215.78	8.141%	$233.3466	$233.35	$233.35	$233.30
Purchase #3	$146.62	8.203%	$158.6472	$158.65	$158.65	$158.60
Purchase #4	$83.94	10.727%	$92.9442	$92.94	$92.95	$92.90
Purchase #5	$82.60	3.334%	$85.3539	$85.35	$85.35	$85.40
Purchase #6	$80.38	10.726%	$89.0016	$89.00	$89.00	$89.00
Purchase #7	$45.50	10.263%	$50.1697	$50.17	$50.15	$50.20
7 purchase totals =	$817.07		$890.2714	$890.27	$890.25	$890.20