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	$115.45	6.676%	$123.1574	$123.16	$123.15	$123.20
Purchase #2	$178.56	11.149%	$198.4677	$198.47	$198.45	$198.50
Purchase #3	$122.97	11.804%	$137.4854	$137.49	$137.50	$137.50
Purchase #4	$45.47	8.490%	$49.3304	$49.33	$49.35	$49.30
Purchase #5	$209.86	3.509%	$217.224	$217.22	$217.20	$217.20
Purchase #6	$225.94	11.489%	$251.8982	$251.90	$251.90	$251.90
Purchase #7	$35.86	12.367%	$40.2948	$40.29	$40.30	$40.30
7 purchase totals =	$934.11		$1,017.8579	$1,017.86	$1,017.85	$1,017.90