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	$73.52	13.828%	$83.6863	$83.69	$83.70	$83.70
Purchase #2	$56.76	5.230%	$59.7285	$59.73	$59.75	$59.70
Purchase #3	$118.33	10.292%	$130.5085	$130.51	$130.50	$130.50
Purchase #4	$113.83	12.350%	$127.888	$127.89	$127.90	$127.90
Purchase #5	$222.81	6.486%	$237.2615	$237.26	$237.25	$237.30
Purchase #6	$132.70	8.308%	$143.7247	$143.72	$143.70	$143.70
Purchase #7	$31.53	9.721%	$34.595	$34.60	$34.60	$34.60
7 purchase totals =	$749.48		$817.3925	$817.40	$817.40	$817.40