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	$152.86	12.168%	$171.46	$171.46	$171.45	$171.50
Purchase #2	$63.48	12.191%	$71.2188	$71.22	$71.20	$71.20
Purchase #3	$198.53	7.683%	$213.7831	$213.78	$213.80	$213.80
Purchase #4	$7.93	7.453%	$8.521	$8.52	$8.50	$8.50
Purchase #5	$226.52	13.635%	$257.406	$257.41	$257.40	$257.40
Purchase #6	$59.41	3.406%	$61.4335	$61.43	$61.45	$61.40
Purchase #7	$134.94	11.351%	$150.257	$150.26	$150.25	$150.30
7 purchase totals =	$843.67		$934.0794	$934.08	$934.05	$934.10