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	$134.41	12.790%	$151.601	$151.60	$151.60	$151.60
Purchase #2	$138.71	7.323%	$148.8677	$148.87	$148.85	$148.90
Purchase #3	$47.62	5.753%	$50.3596	$50.36	$50.35	$50.40
Purchase #4	$41.30	9.518%	$45.2309	$45.23	$45.25	$45.20
Purchase #5	$68.25	12.606%	$76.8536	$76.85	$76.85	$76.90
Purchase #6	$17.77	11.857%	$19.877	$19.88	$19.90	$19.90
Purchase #7	$38.58	10.547%	$42.649	$42.65	$42.65	$42.60
7 purchase totals =	$486.64		$535.4388	$535.44	$535.45	$535.50