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	$77.96	13.589%	$88.554	$88.55	$88.55	$88.60
Purchase #2	$151.92	10.328%	$167.6103	$167.61	$167.60	$167.60
Purchase #3	$33.49	3.359%	$34.6149	$34.61	$34.60	$34.60
Purchase #4	$227.35	5.756%	$240.4363	$240.44	$240.45	$240.40
Purchase #5	$50.27	7.851%	$54.2167	$54.22	$54.20	$54.20
Purchase #6	$18.86	5.600%	$19.9162	$19.92	$19.90	$19.90
Purchase #7	$85.71	4.761%	$89.7907	$89.79	$89.80	$89.80
7 purchase totals =	$645.56		$695.1391	$695.14	$695.10	$695.10