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	$35.65	12.585%	$40.1366	$40.14	$40.15	$40.10
Purchase #2	$152.57	8.804%	$166.0023	$166.00	$166.00	$166.00
Purchase #3	$63.90	7.260%	$68.5391	$68.54	$68.55	$68.50
Purchase #4	$178.45	11.250%	$198.5256	$198.53	$198.55	$198.50
Purchase #5	$32.73	8.452%	$35.4963	$35.50	$35.50	$35.50
Purchase #6	$43.81	4.336%	$45.7096	$45.71	$45.70	$45.70
Purchase #7	$137.37	13.132%	$155.4094	$155.41	$155.40	$155.40
7 purchase totals =	$644.48		$709.8189	$709.83	$709.85	$709.70