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	$126.50	12.288%	$142.0443	$142.04	$142.05	$142.00
Purchase #2	$103.64	7.176%	$111.0772	$111.08	$111.10	$111.10
Purchase #3	$63.74	9.278%	$69.6538	$69.65	$69.65	$69.70
Purchase #4	$10.46	9.103%	$11.4122	$11.41	$11.40	$11.40
Purchase #5	$198.44	9.401%	$217.0953	$217.10	$217.10	$217.10
Purchase #6	$81.85	11.639%	$91.3765	$91.38	$91.40	$91.40
Purchase #7	$50.86	13.818%	$57.8878	$57.89	$57.90	$57.90
7 purchase totals =	$635.49		$700.5471	$700.55	$700.60	$700.60