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	$134.32	5.204%	$141.31	$141.31	$141.30	$141.30
Purchase #2	$152.81	13.398%	$173.2835	$173.28	$173.30	$173.30
Purchase #3	$174.61	3.385%	$180.5205	$180.52	$180.50	$180.50
Purchase #4	$35.41	10.835%	$39.2467	$39.25	$39.25	$39.20
Purchase #5	$78.99	13.415%	$89.5865	$89.59	$89.60	$89.60
Purchase #6	$178.43	4.342%	$186.1774	$186.18	$186.20	$186.20
Purchase #7	$138.66	6.294%	$147.3873	$147.39	$147.40	$147.40
7 purchase totals =	$893.23		$957.5119	$957.52	$957.55	$957.50