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	$54.47	5.494%	$57.4626	$57.46	$57.45	$57.50
Purchase #2	$95.57	9.203%	$104.3653	$104.37	$104.35	$104.40
Purchase #3	$176.52	4.679%	$184.7794	$184.78	$184.80	$184.80
Purchase #4	$82.31	10.359%	$90.8365	$90.84	$90.85	$90.80
Purchase #5	$218.68	11.534%	$243.9026	$243.90	$243.90	$243.90
Purchase #6	$152.25	13.393%	$172.6408	$172.64	$172.65	$172.60
Purchase #7	$164.80	4.868%	$172.8225	$172.82	$172.80	$172.80
7 purchase totals =	$944.60		$1,026.8097	$1,026.81	$1,026.80	$1,026.80