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	$123.28	3.764%	$127.9203	$127.92	$127.90	$127.90
Purchase #2	$55.75	6.737%	$59.5059	$59.51	$59.50	$59.50
Purchase #3	$71.82	10.134%	$79.0982	$79.10	$79.10	$79.10
Purchase #4	$205.52	8.455%	$222.8967	$222.90	$222.90	$222.90
Purchase #5	$70.54	12.690%	$79.4915	$79.49	$79.50	$79.50
Purchase #6	$67.89	10.367%	$74.9282	$74.93	$74.95	$74.90
Purchase #7	$5.25	9.704%	$5.7595	$5.76	$5.75	$5.80
7 purchase totals =	$600.05		$649.6003	$649.61	$649.60	$649.60