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	$136.40	6.177%	$144.8254	$144.83	$144.85	$144.80
Purchase #2	$85.51	5.574%	$90.2763	$90.28	$90.30	$90.30
Purchase #3	$213.98	10.680%	$236.8331	$236.83	$236.85	$236.80
Purchase #4	$50.28	3.474%	$52.0267	$52.03	$52.05	$52.00
Purchase #5	$78.99	12.145%	$88.5833	$88.58	$88.60	$88.60
Purchase #6	$178.55	4.723%	$186.9829	$186.98	$187.00	$187.00
Purchase #7	$127.56	3.349%	$131.832	$131.83	$131.85	$131.80
7 purchase totals =	$871.27		$931.3597	$931.36	$931.50	$931.30