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	$234.31	3.138%	$241.6626	$241.66	$241.65	$241.70
Purchase #2	$100.68	10.598%	$111.3501	$111.35	$111.35	$111.40
Purchase #3	$93.62	12.150%	$104.9948	$104.99	$105.00	$105.00
Purchase #4	$35.50	13.814%	$40.404	$40.40	$40.40	$40.40
Purchase #5	$142.83	10.871%	$158.357	$158.36	$158.35	$158.40
Purchase #6	$157.42	12.827%	$177.6123	$177.61	$177.60	$177.60
Purchase #7	$73.40	8.855%	$79.8996	$79.90	$79.90	$79.90
7 purchase totals =	$837.76		$914.2804	$914.27	$914.25	$914.40