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	$243.40	6.595%	$259.4522	$259.45	$259.45	$259.50
Purchase #2	$126.56	10.739%	$140.1513	$140.15	$140.15	$140.20
Purchase #3	$160.34	3.661%	$166.21	$166.21	$166.20	$166.20
Purchase #4	$113.61	8.273%	$123.009	$123.01	$123.00	$123.00
Purchase #5	$249.30	3.132%	$257.1081	$257.11	$257.10	$257.10
Purchase #6	$48.94	11.307%	$54.4736	$54.47	$54.45	$54.50
Purchase #7	$224.64	6.165%	$238.4891	$238.49	$238.50	$238.50
7 purchase totals =	$1,166.79		$1,238.8933	$1,238.89	$1,238.85	$1,239.00