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	$82.84	7.852%	$89.3446	$89.34	$89.35	$89.30
Purchase #2	$225.44	11.376%	$251.0861	$251.09	$251.10	$251.10
Purchase #3	$28.46	9.857%	$31.2653	$31.27	$31.25	$31.30
Purchase #4	$248.71	13.139%	$281.388	$281.39	$281.40	$281.40
Purchase #5	$92.67	10.266%	$102.1835	$102.18	$102.20	$102.20
Purchase #6	$124.30	5.493%	$131.1278	$131.13	$131.15	$131.10
Purchase #7	$104.47	8.701%	$113.5599	$113.56	$113.55	$113.60
7 purchase totals =	$906.89		$999.9552	$999.96	$1,000.00	$1,000.00