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	$94.48	6.731%	$100.8394	$100.84	$100.85	$100.80
Purchase #2	$91.59	12.781%	$103.2961	$103.30	$103.30	$103.30
Purchase #3	$82.43	10.268%	$90.8939	$90.89	$90.90	$90.90
Purchase #4	$243.55	13.166%	$275.6158	$275.62	$275.60	$275.60
Purchase #5	$123.86	12.104%	$138.852	$138.85	$138.85	$138.90
Purchase #6	$120.67	8.582%	$131.0259	$131.03	$131.05	$131.00
Purchase #7	$108.42	13.136%	$122.6621	$122.66	$122.65	$122.70
7 purchase totals =	$865.00		$963.1852	$963.19	$963.20	$963.20