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	$248.86	8.231%	$269.3437	$269.34	$269.35	$269.30
Purchase #2	$97.34	7.504%	$104.6444	$104.64	$104.65	$104.60
Purchase #3	$120.91	9.638%	$132.5633	$132.56	$132.55	$132.60
Purchase #4	$120.83	4.508%	$126.277	$126.28	$126.30	$126.30
Purchase #5	$31.30	8.503%	$33.9614	$33.96	$33.95	$34.00
Purchase #6	$180.41	6.169%	$191.5395	$191.54	$191.55	$191.50
Purchase #7	$200.63	10.436%	$221.5677	$221.57	$221.55	$221.60
7 purchase totals =	$1,000.28		$1,079.8970	$1,079.89	$1,079.90	$1,079.90