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	$110.89	10.305%	$122.3172	$122.32	$122.30	$122.30
Purchase #2	$171.41	4.692%	$179.4526	$179.45	$179.45	$179.50
Purchase #3	$103.55	12.138%	$116.1189	$116.12	$116.10	$116.10
Purchase #4	$199.93	10.591%	$221.1046	$221.10	$221.10	$221.10
Purchase #5	$215.25	13.298%	$243.8739	$243.87	$243.85	$243.90
Purchase #6	$73.51	11.488%	$81.9548	$81.95	$81.95	$82.00
Purchase #7	$12.27	13.632%	$13.9426	$13.94	$13.95	$13.90
7 purchase totals =	$886.81		$978.7646	$978.75	$978.70	$978.80