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	$17.28	10.808%	$19.1476	$19.15	$19.15	$19.10
Purchase #2	$194.45	10.785%	$215.4214	$215.42	$215.40	$215.40
Purchase #3	$72.43	8.718%	$78.7444	$78.74	$78.75	$78.70
Purchase #4	$167.42	11.181%	$186.1392	$186.14	$186.15	$186.10
Purchase #5	$123.36	7.602%	$132.7378	$132.74	$132.75	$132.70
Purchase #6	$95.57	8.743%	$103.9257	$103.93	$103.95	$103.90
Purchase #7	$78.90	5.596%	$83.3152	$83.32	$83.30	$83.30
7 purchase totals =	$749.41		$819.4313	$819.44	$819.45	$819.20