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	$226.59	10.150%	$249.5889	$249.59	$249.60	$249.60
Purchase #2	$187.61	4.108%	$195.317	$195.32	$195.30	$195.30
Purchase #3	$83.59	12.852%	$94.333	$94.33	$94.35	$94.30
Purchase #4	$134.94	3.576%	$139.7655	$139.77	$139.75	$139.80
Purchase #5	$86.85	10.341%	$95.8312	$95.83	$95.85	$95.80
Purchase #6	$34.27	12.300%	$38.4852	$38.49	$38.50	$38.50
Purchase #7	$19.49	12.850%	$21.9945	$21.99	$22.00	$22.00
7 purchase totals =	$773.34		$835.3153	$835.32	$835.35	$835.30