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	$11.60	4.772%	$12.1536	$12.15	$12.15	$12.20
Purchase #2	$185.42	12.276%	$208.1822	$208.18	$208.20	$208.20
Purchase #3	$131.69	4.282%	$137.329	$137.33	$137.35	$137.30
Purchase #4	$152.61	9.147%	$166.5692	$166.57	$166.55	$166.60
Purchase #5	$56.71	8.325%	$61.4311	$61.43	$61.45	$61.40
Purchase #6	$169.69	8.473%	$184.0678	$184.07	$184.05	$184.10
Purchase #7	$18.85	3.847%	$19.5752	$19.58	$19.60	$19.60
7 purchase totals =	$726.57		$789.3081	$789.31	$789.35	$789.40