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	$30.41	13.758%	$34.5938	$34.59	$34.60	$34.60
Purchase #2	$235.46	12.151%	$264.0707	$264.07	$264.05	$264.10
Purchase #3	$33.62	11.373%	$37.4436	$37.44	$37.45	$37.40
Purchase #4	$100.38	7.205%	$107.6124	$107.61	$107.60	$107.60
Purchase #5	$134.79	4.316%	$140.6075	$140.61	$140.60	$140.60
Purchase #6	$72.47	11.379%	$80.7164	$80.72	$80.70	$80.70
Purchase #7	$177.46	3.845%	$184.2833	$184.28	$184.30	$184.30
7 purchase totals =	$784.59		$849.3277	$849.32	$849.30	$849.30