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	$79.88	12.859%	$90.1518	$90.15	$90.15	$90.20
Purchase #2	$135.80	10.833%	$150.5112	$150.51	$150.50	$150.50
Purchase #3	$56.78	10.140%	$62.5375	$62.54	$62.55	$62.50
Purchase #4	$239.79	4.849%	$251.4174	$251.42	$251.40	$251.40
Purchase #5	$208.67	13.496%	$236.8321	$236.83	$236.85	$236.80
Purchase #6	$245.95	4.620%	$257.3129	$257.31	$257.30	$257.30
Purchase #7	$225.56	3.528%	$233.5178	$233.52	$233.50	$233.50
7 purchase totals =	$1,192.43		$1,282.2807	$1,282.28	$1,282.25	$1,282.20