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	$227.32	10.321%	$250.7817	$250.78	$250.80	$250.80
Purchase #2	$39.84	3.174%	$41.1045	$41.10	$41.10	$41.10
Purchase #3	$35.35	6.183%	$37.5357	$37.54	$37.55	$37.50
Purchase #4	$111.95	8.634%	$121.6158	$121.62	$121.60	$121.60
Purchase #5	$196.66	3.192%	$202.9374	$202.94	$202.95	$202.90
Purchase #6	$160.59	7.649%	$172.8735	$172.87	$172.85	$172.90
Purchase #7	$171.51	11.307%	$190.9026	$190.90	$190.90	$190.90
7 purchase totals =	$943.22		$1,017.7512	$1,017.75	$1,017.75	$1,017.70