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	$26.78	11.578%	$29.8806	$29.88	$29.90	$29.90
Purchase #2	$212.81	5.103%	$223.6697	$223.67	$223.65	$223.70
Purchase #3	$156.45	3.535%	$161.9805	$161.98	$162.00	$162.00
Purchase #4	$138.81	3.458%	$143.61	$143.61	$143.60	$143.60
Purchase #5	$170.32	6.236%	$180.9412	$180.94	$180.95	$180.90
Purchase #6	$213.86	12.102%	$239.7413	$239.74	$239.75	$239.70
Purchase #7	$82.56	7.849%	$89.0401	$89.04	$89.05	$89.00
7 purchase totals =	$1,001.59		$1,068.8634	$1,068.86	$1,068.90	$1,068.80