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	$126.62	13.167%	$143.2921	$143.29	$143.30	$143.30
Purchase #2	$220.61	11.482%	$245.9404	$245.94	$245.95	$245.90
Purchase #3	$63.30	4.237%	$65.982	$65.98	$66.00	$66.00
Purchase #4	$167.54	11.245%	$186.3799	$186.38	$186.40	$186.40
Purchase #5	$152.83	9.170%	$166.8445	$166.84	$166.85	$166.80
Purchase #6	$62.82	5.267%	$66.1287	$66.13	$66.15	$66.10
Purchase #7	$96.92	3.670%	$100.477	$100.48	$100.50	$100.50
7 purchase totals =	$890.64		$975.0446	$975.04	$975.15	$975.00