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	$19.35	5.870%	$20.4858	$20.49	$20.50	$20.50
Purchase #2	$217.37	12.771%	$245.1303	$245.13	$245.15	$245.10
Purchase #3	$41.38	9.526%	$45.3219	$45.32	$45.30	$45.30
Purchase #4	$6.82	11.245%	$7.5869	$7.59	$7.60	$7.60
Purchase #5	$164.33	12.498%	$184.868	$184.87	$184.85	$184.90
Purchase #6	$177.62	4.147%	$184.9859	$184.99	$185.00	$185.00
Purchase #7	$123.63	5.785%	$130.782	$130.78	$130.80	$130.80
7 purchase totals =	$750.50		$819.1608	$819.17	$819.20	$819.20