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	$101.92	9.735%	$111.8419	$111.84	$111.85	$111.80
Purchase #2	$44.25	11.847%	$49.4923	$49.49	$49.50	$49.50
Purchase #3	$192.31	8.385%	$208.4352	$208.44	$208.45	$208.40
Purchase #4	$56.55	8.409%	$61.3053	$61.31	$61.30	$61.30
Purchase #5	$74.35	3.191%	$76.7225	$76.72	$76.70	$76.70
Purchase #6	$94.29	8.782%	$102.5705	$102.57	$102.55	$102.60
Purchase #7	$29.63	6.465%	$31.5456	$31.55	$31.55	$31.50
7 purchase totals =	$593.30		$641.9133	$641.92	$641.90	$641.80