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	$146.51	12.461%	$164.7666	$164.77	$164.75	$164.80
Purchase #2	$142.84	5.105%	$150.132	$150.13	$150.15	$150.10
Purchase #3	$73.93	8.179%	$79.9767	$79.98	$80.00	$80.00
Purchase #4	$103.96	8.285%	$112.5731	$112.57	$112.55	$112.60
Purchase #5	$89.87	11.528%	$100.2302	$100.23	$100.25	$100.20
Purchase #6	$189.42	3.178%	$195.4398	$195.44	$195.45	$195.40
Purchase #7	$160.82	3.752%	$166.854	$166.85	$166.85	$166.90
7 purchase totals =	$907.35		$969.9724	$969.97	$970.00	$970.00