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	$184.86	11.197%	$205.5588	$205.56	$205.55	$205.60
Purchase #2	$35.68	10.845%	$39.5495	$39.55	$39.55	$39.50
Purchase #3	$203.80	10.557%	$225.3152	$225.32	$225.30	$225.30
Purchase #4	$170.90	11.717%	$190.9244	$190.92	$190.90	$190.90
Purchase #5	$27.84	4.504%	$29.0939	$29.09	$29.10	$29.10
Purchase #6	$41.54	10.466%	$45.8876	$45.89	$45.90	$45.90
Purchase #7	$71.48	13.685%	$81.262	$81.26	$81.25	$81.30
7 purchase totals =	$736.10		$817.5914	$817.59	$817.55	$817.60