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	$55.80	6.119%	$59.2144	$59.21	$59.20	$59.20
Purchase #2	$226.51	3.704%	$234.8999	$234.90	$234.90	$234.90
Purchase #3	$60.36	8.700%	$65.6113	$65.61	$65.60	$65.60
Purchase #4	$93.80	12.282%	$105.3205	$105.32	$105.30	$105.30
Purchase #5	$50.47	10.175%	$55.6053	$55.61	$55.60	$55.60
Purchase #6	$155.68	11.786%	$174.0284	$174.03	$174.05	$174.00
Purchase #7	$113.89	3.449%	$117.8181	$117.82	$117.80	$117.80
7 purchase totals =	$756.51		$812.4979	$812.50	$812.45	$812.40