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	$70.97	3.200%	$73.241	$73.24	$73.25	$73.20
Purchase #2	$31.52	7.357%	$33.8389	$33.84	$33.85	$33.80
Purchase #3	$77.25	12.330%	$86.7749	$86.77	$86.75	$86.80
Purchase #4	$27.96	13.451%	$31.7209	$31.72	$31.70	$31.70
Purchase #5	$127.99	11.314%	$142.4708	$142.47	$142.45	$142.50
Purchase #6	$20.40	7.636%	$21.9577	$21.96	$21.95	$22.00
Purchase #7	$121.29	8.219%	$131.2588	$131.26	$131.25	$131.30
7 purchase totals =	$477.38		$521.2630	$521.26	$521.20	$521.30