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	$59.90	11.515%	$66.7975	$66.80	$66.80	$66.80
Purchase #2	$40.26	7.136%	$43.133	$43.13	$43.15	$43.10
Purchase #3	$58.60	4.762%	$61.3905	$61.39	$61.40	$61.40
Purchase #4	$232.46	10.512%	$256.8962	$256.90	$256.90	$256.90
Purchase #5	$156.44	9.431%	$171.1939	$171.19	$171.20	$171.20
Purchase #6	$7.25	3.500%	$7.5038	$7.50	$7.50	$7.50
Purchase #7	$35.97	13.128%	$40.6921	$40.69	$40.70	$40.70
7 purchase totals =	$590.88		$647.6070	$647.60	$647.65	$647.60