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	$14.30	8.548%	$15.5224	$15.52	$15.50	$15.50
Purchase #2	$151.89	9.387%	$166.1479	$166.15	$166.15	$166.10
Purchase #3	$146.25	6.208%	$155.3292	$155.33	$155.35	$155.30
Purchase #4	$66.84	13.540%	$75.8901	$75.89	$75.90	$75.90
Purchase #5	$165.69	11.689%	$185.0575	$185.06	$185.05	$185.10
Purchase #6	$63.86	9.826%	$70.1349	$70.13	$70.15	$70.10
Purchase #7	$41.56	13.107%	$47.0073	$47.01	$47.00	$47.00
7 purchase totals =	$650.39		$715.0893	$715.09	$715.10	$715.00