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	$117.92	5.482%	$124.3844	$124.38	$124.40	$124.40
Purchase #2	$167.38	10.769%	$185.4052	$185.41	$185.40	$185.40
Purchase #3	$137.39	10.593%	$151.9437	$151.94	$151.95	$151.90
Purchase #4	$221.60	13.815%	$252.214	$252.21	$252.20	$252.20
Purchase #5	$10.78	13.114%	$12.1937	$12.19	$12.20	$12.20
Purchase #6	$50.34	10.166%	$55.4576	$55.46	$55.45	$55.50
Purchase #7	$212.36	3.863%	$220.5635	$220.56	$220.55	$220.60
7 purchase totals =	$917.77		$1,002.1621	$1,002.15	$1,002.15	$1,002.20