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	$56.25	3.484%	$58.2098	$58.21	$58.20	$58.20
Purchase #2	$151.89	13.493%	$172.3845	$172.38	$172.40	$172.40
Purchase #3	$248.56	4.560%	$259.8943	$259.89	$259.90	$259.90
Purchase #4	$220.70	8.185%	$238.7643	$238.76	$238.75	$238.80
Purchase #5	$53.98	10.734%	$59.7742	$59.77	$59.75	$59.80
Purchase #6	$51.39	11.359%	$57.2274	$57.23	$57.25	$57.20
Purchase #7	$76.83	12.544%	$86.4676	$86.47	$86.45	$86.50
7 purchase totals =	$859.60		$932.7221	$932.71	$932.70	$932.80