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	$123.55	13.238%	$139.9055	$139.91	$139.90	$139.90
Purchase #2	$64.63	3.290%	$66.7563	$66.76	$66.75	$66.80
Purchase #3	$21.63	10.530%	$23.9076	$23.91	$23.90	$23.90
Purchase #4	$55.41	11.651%	$61.8658	$61.87	$61.85	$61.90
Purchase #5	$196.46	6.756%	$209.7328	$209.73	$209.75	$209.70
Purchase #6	$156.64	7.661%	$168.6402	$168.64	$168.65	$168.60
Purchase #7	$241.55	11.445%	$269.1954	$269.20	$269.20	$269.20
7 purchase totals =	$859.87		$940.0036	$940.02	$940.00	$940.00