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	$59.89	6.734%	$63.923	$63.92	$63.90	$63.90
Purchase #2	$16.60	5.449%	$17.5045	$17.50	$17.50	$17.50
Purchase #3	$164.52	9.716%	$180.5048	$180.50	$180.50	$180.50
Purchase #4	$130.43	7.734%	$140.5175	$140.52	$140.50	$140.50
Purchase #5	$75.36	3.726%	$78.1679	$78.17	$78.15	$78.20
Purchase #6	$10.89	9.145%	$11.8859	$11.89	$11.90	$11.90
Purchase #7	$80.80	10.127%	$88.9826	$88.98	$89.00	$89.00
7 purchase totals =	$538.49		$581.4862	$581.48	$581.45	$581.50