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	$99.46	5.839%	$105.2675	$105.27	$105.25	$105.30
Purchase #2	$82.51	8.339%	$89.3905	$89.39	$89.40	$89.40
Purchase #3	$107.46	8.818%	$116.9358	$116.94	$116.95	$116.90
Purchase #4	$120.98	8.348%	$131.0794	$131.08	$131.10	$131.10
Purchase #5	$213.48	7.577%	$229.6554	$229.66	$229.65	$229.70
Purchase #6	$126.41	4.309%	$131.857	$131.86	$131.85	$131.90
Purchase #7	$97.93	11.678%	$109.3663	$109.37	$109.35	$109.40
7 purchase totals =	$848.23		$913.5519	$913.57	$913.55	$913.70