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	$98.94	4.728%	$103.6179	$103.62	$103.60	$103.60
Purchase #2	$136.28	13.592%	$154.8032	$154.80	$154.80	$154.80
Purchase #3	$250.42	11.493%	$279.2008	$279.20	$279.20	$279.20
Purchase #4	$90.74	10.540%	$100.304	$100.30	$100.30	$100.30
Purchase #5	$63.90	11.223%	$71.0715	$71.07	$71.05	$71.10
Purchase #6	$232.51	4.638%	$243.2938	$243.29	$243.30	$243.30
Purchase #7	$15.81	7.134%	$16.9379	$16.94	$16.95	$16.90
7 purchase totals =	$888.60		$969.2291	$969.22	$969.20	$969.20