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	$11.55	7.779%	$12.4485	$12.45	$12.45	$12.40
Purchase #2	$198.58	8.739%	$215.9339	$215.93	$215.95	$215.90
Purchase #3	$216.76	7.670%	$233.3855	$233.39	$233.40	$233.40
Purchase #4	$92.79	6.377%	$98.7072	$98.71	$98.70	$98.70
Purchase #5	$145.43	3.297%	$150.2248	$150.22	$150.20	$150.20
Purchase #6	$244.63	4.419%	$255.4402	$255.44	$255.45	$255.40
Purchase #7	$188.57	9.531%	$206.5426	$206.54	$206.55	$206.50
7 purchase totals =	$1,098.31		$1,172.6827	$1,172.68	$1,172.70	$1,172.50