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	$18.57	13.425%	$21.063	$21.06	$21.05	$21.10
Purchase #2	$76.59	13.712%	$87.092	$87.09	$87.10	$87.10
Purchase #3	$55.53	7.812%	$59.868	$59.87	$59.85	$59.90
Purchase #4	$22.62	11.455%	$25.2111	$25.21	$25.20	$25.20
Purchase #5	$195.40	12.559%	$219.9403	$219.94	$219.95	$219.90
Purchase #6	$58.89	6.864%	$62.9322	$62.93	$62.95	$62.90
Purchase #7	$40.71	5.749%	$43.0504	$43.05	$43.05	$43.10
7 purchase totals =	$468.31		$519.1570	$519.15	$519.15	$519.20