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	$45.59	12.371%	$51.2299	$51.23	$51.25	$51.20
Purchase #2	$79.72	10.593%	$88.1647	$88.16	$88.15	$88.20
Purchase #3	$166.89	10.170%	$183.8627	$183.86	$183.85	$183.90
Purchase #4	$52.75	6.595%	$56.2289	$56.23	$56.25	$56.20
Purchase #5	$37.93	11.790%	$42.4019	$42.40	$42.40	$42.40
Purchase #6	$161.88	11.336%	$180.2307	$180.23	$180.25	$180.20
Purchase #7	$218.47	8.509%	$237.0596	$237.06	$237.05	$237.10
7 purchase totals =	$763.23		$839.1784	$839.17	$839.20	$839.20