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	$240.34	4.779%	$251.8258	$251.83	$251.85	$251.80
Purchase #2	$128.82	7.574%	$138.5768	$138.58	$138.60	$138.60
Purchase #3	$55.96	11.432%	$62.3573	$62.36	$62.35	$62.40
Purchase #4	$132.25	12.156%	$148.3263	$148.33	$148.35	$148.30
Purchase #5	$216.63	13.845%	$246.6224	$246.62	$246.60	$246.60
Purchase #6	$173.34	6.758%	$185.0543	$185.05	$185.05	$185.10
Purchase #7	$155.72	7.694%	$167.7011	$167.70	$167.70	$167.70
7 purchase totals =	$1,103.06		$1,200.4640	$1,200.47	$1,200.50	$1,200.50