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	$45.96	11.384%	$51.1921	$51.19	$51.20	$51.20
Purchase #2	$126.32	10.322%	$139.3588	$139.36	$139.35	$139.40
Purchase #3	$17.63	6.426%	$18.7629	$18.76	$18.75	$18.80
Purchase #4	$207.52	9.835%	$227.9296	$227.93	$227.95	$227.90
Purchase #5	$104.36	11.624%	$116.4908	$116.49	$116.50	$116.50
Purchase #6	$233.81	13.185%	$264.6378	$264.64	$264.65	$264.60
Purchase #7	$54.86	8.696%	$59.6306	$59.63	$59.65	$59.60
7 purchase totals =	$790.46		$878.0026	$878.00	$878.05	$878.00