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	$134.69	3.703%	$139.6776	$139.68	$139.70	$139.70
Purchase #2	$100.34	4.234%	$104.5884	$104.59	$104.60	$104.60
Purchase #3	$130.96	10.196%	$144.3127	$144.31	$144.30	$144.30
Purchase #4	$167.44	10.659%	$185.2874	$185.29	$185.30	$185.30
Purchase #5	$119.62	6.632%	$127.5532	$127.55	$127.55	$127.60
Purchase #6	$101.81	9.628%	$111.6123	$111.61	$111.60	$111.60
Purchase #7	$27.77	6.397%	$29.5464	$29.55	$29.55	$29.50
7 purchase totals =	$782.63		$842.5780	$842.58	$842.60	$842.60