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	$94.38	6.674%	$100.6789	$100.68	$100.70	$100.70
Purchase #2	$103.41	6.793%	$110.4346	$110.43	$110.45	$110.40
Purchase #3	$176.72	8.107%	$191.0467	$191.05	$191.05	$191.00
Purchase #4	$34.77	11.449%	$38.7508	$38.75	$38.75	$38.80
Purchase #5	$187.45	13.772%	$213.2656	$213.27	$213.25	$213.30
Purchase #6	$80.59	12.785%	$90.8934	$90.89	$90.90	$90.90
Purchase #7	$190.77	3.346%	$197.1532	$197.15	$197.15	$197.20
7 purchase totals =	$868.09		$942.2232	$942.22	$942.25	$942.30