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	$213.32	10.653%	$236.045	$236.05	$236.05	$236.00
Purchase #2	$98.51	5.731%	$104.1556	$104.16	$104.15	$104.20
Purchase #3	$232.87	4.143%	$242.5178	$242.52	$242.50	$242.50
Purchase #4	$211.70	4.312%	$220.8285	$220.83	$220.85	$220.80
Purchase #5	$28.63	8.765%	$31.1394	$31.14	$31.15	$31.10
Purchase #6	$37.72	12.444%	$42.4139	$42.41	$42.40	$42.40
Purchase #7	$87.97	13.357%	$99.7202	$99.72	$99.70	$99.70
7 purchase totals =	$910.72		$976.8204	$976.83	$976.80	$976.70