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	$35.35	8.717%	$38.4315	$38.43	$38.45	$38.40
Purchase #2	$196.26	6.606%	$209.2249	$209.22	$209.20	$209.20
Purchase #3	$234.81	6.645%	$250.4131	$250.41	$250.40	$250.40
Purchase #4	$95.27	10.602%	$105.3705	$105.37	$105.35	$105.40
Purchase #5	$71.64	8.720%	$77.887	$77.89	$77.90	$77.90
Purchase #6	$99.58	10.500%	$110.0359	$110.04	$110.05	$110.00
Purchase #7	$130.87	11.246%	$145.5876	$145.59	$145.60	$145.60
7 purchase totals =	$863.78		$936.9505	$936.95	$936.95	$936.90