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	$22.95	7.786%	$24.7369	$24.74	$24.75	$24.70
Purchase #2	$127.51	5.222%	$134.1686	$134.17	$134.15	$134.20
Purchase #3	$38.62	9.628%	$42.3383	$42.34	$42.35	$42.30
Purchase #4	$74.59	9.429%	$81.6231	$81.62	$81.60	$81.60
Purchase #5	$210.70	4.139%	$219.4209	$219.42	$219.40	$219.40
Purchase #6	$123.57	6.487%	$131.586	$131.59	$131.60	$131.60
Purchase #7	$12.46	11.494%	$13.8922	$13.89	$13.90	$13.90
7 purchase totals =	$610.40		$647.7660	$647.77	$647.75	$647.70