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	$51.80	5.168%	$54.477	$54.48	$54.50	$54.50
Purchase #2	$124.61	5.711%	$131.7265	$131.73	$131.75	$131.70
Purchase #3	$60.96	7.517%	$65.5424	$65.54	$65.55	$65.50
Purchase #4	$214.82	8.641%	$233.3826	$233.38	$233.40	$233.40
Purchase #5	$69.70	11.129%	$77.4569	$77.46	$77.45	$77.50
Purchase #6	$163.80	4.683%	$171.4708	$171.47	$171.45	$171.50
Purchase #7	$16.61	9.261%	$18.1483	$18.15	$18.15	$18.10
7 purchase totals =	$702.30		$752.2045	$752.21	$752.25	$752.20