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	$102.71	6.561%	$109.4488	$109.45	$109.45	$109.40
Purchase #2	$224.88	4.714%	$235.4808	$235.48	$235.50	$235.50
Purchase #3	$222.87	4.721%	$233.3917	$233.39	$233.40	$233.40
Purchase #4	$189.78	11.531%	$211.6635	$211.66	$211.65	$211.70
Purchase #5	$176.83	13.654%	$200.9744	$200.97	$200.95	$201.00
Purchase #6	$248.59	10.427%	$274.5105	$274.51	$274.50	$274.50
Purchase #7	$40.50	6.826%	$43.2645	$43.26	$43.25	$43.30
7 purchase totals =	$1,206.16		$1,308.7342	$1,308.72	$1,308.70	$1,308.80