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	$187.79	6.241%	$199.51	$199.51	$199.50	$199.50
Purchase #2	$196.63	8.592%	$213.5244	$213.52	$213.50	$213.50
Purchase #3	$131.75	7.827%	$142.0621	$142.06	$142.05	$142.10
Purchase #4	$35.49	9.470%	$38.8509	$38.85	$38.85	$38.90
Purchase #5	$53.37	12.570%	$60.0786	$60.08	$60.10	$60.10
Purchase #6	$69.62	11.278%	$77.4717	$77.47	$77.45	$77.50
Purchase #7	$134.92	7.398%	$144.9014	$144.90	$144.90	$144.90
7 purchase totals =	$809.57		$876.3991	$876.39	$876.35	$876.50