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	$46.73	8.783%	$50.8343	$50.83	$50.85	$50.80
Purchase #2	$217.55	11.687%	$242.9751	$242.98	$243.00	$243.00
Purchase #3	$243.90	6.546%	$259.8657	$259.87	$259.85	$259.90
Purchase #4	$113.30	13.600%	$128.7088	$128.71	$128.70	$128.70
Purchase #5	$118.30	12.474%	$133.0567	$133.06	$133.05	$133.10
Purchase #6	$80.69	3.261%	$83.3213	$83.32	$83.30	$83.30
Purchase #7	$92.28	8.700%	$100.3084	$100.31	$100.30	$100.30
7 purchase totals =	$912.75		$999.0703	$999.08	$999.05	$999.10