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	$150.43	6.246%	$159.8259	$159.83	$159.85	$159.80
Purchase #2	$123.89	5.790%	$131.0632	$131.06	$131.05	$131.10
Purchase #3	$196.27	4.190%	$204.4937	$204.49	$204.50	$204.50
Purchase #4	$126.78	7.614%	$136.433	$136.43	$136.45	$136.40
Purchase #5	$95.79	12.585%	$107.8452	$107.85	$107.85	$107.80
Purchase #6	$228.84	5.458%	$241.3301	$241.33	$241.35	$241.30
Purchase #7	$18.60	11.228%	$20.6884	$20.69	$20.70	$20.70
7 purchase totals =	$940.60		$1,001.6795	$1,001.68	$1,001.75	$1,001.60