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	$30.99	8.350%	$33.5777	$33.58	$33.60	$33.60
Purchase #2	$18.88	9.647%	$20.7014	$20.70	$20.70	$20.70
Purchase #3	$180.98	8.805%	$196.9153	$196.92	$196.90	$196.90
Purchase #4	$242.61	11.311%	$270.0516	$270.05	$270.05	$270.10
Purchase #5	$26.28	4.609%	$27.4912	$27.49	$27.50	$27.50
Purchase #6	$71.57	9.257%	$78.1952	$78.20	$78.20	$78.20
Purchase #7	$37.59	7.797%	$40.5209	$40.52	$40.50	$40.50
7 purchase totals =	$608.90		$667.4533	$667.46	$667.45	$667.50