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	$246.57	5.217%	$259.4336	$259.43	$259.45	$259.40
Purchase #2	$12.51	7.232%	$13.4147	$13.41	$13.40	$13.40
Purchase #3	$127.79	7.832%	$137.7985	$137.80	$137.80	$137.80
Purchase #4	$109.46	8.852%	$119.1494	$119.15	$119.15	$119.10
Purchase #5	$175.61	5.841%	$185.8674	$185.87	$185.85	$185.90
Purchase #6	$90.35	12.152%	$101.3293	$101.33	$101.35	$101.30
Purchase #7	$68.54	6.124%	$72.7374	$72.74	$72.75	$72.70
7 purchase totals =	$830.83		$889.7303	$889.73	$889.75	$889.60