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	$146.39	12.862%	$165.2187	$165.22	$165.20	$165.20
Purchase #2	$116.47	6.613%	$124.1722	$124.17	$124.15	$124.20
Purchase #3	$248.65	3.715%	$257.8873	$257.89	$257.90	$257.90
Purchase #4	$63.96	12.446%	$71.9205	$71.92	$71.90	$71.90
Purchase #5	$24.93	10.348%	$27.5098	$27.51	$27.50	$27.50
Purchase #6	$205.51	10.171%	$226.4124	$226.41	$226.40	$226.40
Purchase #7	$42.29	7.516%	$45.4685	$45.47	$45.45	$45.50
7 purchase totals =	$848.20		$918.5894	$918.59	$918.50	$918.60