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	$11.41	9.516%	$12.4958	$12.50	$12.50	$12.50
Purchase #2	$202.86	7.617%	$218.3118	$218.31	$218.30	$218.30
Purchase #3	$217.46	13.645%	$247.1324	$247.13	$247.15	$247.10
Purchase #4	$75.67	3.502%	$78.32	$78.32	$78.30	$78.30
Purchase #5	$28.72	4.335%	$29.965	$29.97	$29.95	$30.00
Purchase #6	$65.79	13.827%	$74.8868	$74.89	$74.90	$74.90
Purchase #7	$45.98	10.505%	$50.8102	$50.81	$50.80	$50.80
7 purchase totals =	$647.89		$711.9220	$711.93	$711.90	$711.90