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	$64.59	11.137%	$71.7834	$71.78	$71.80	$71.80
Purchase #2	$46.59	12.436%	$52.3839	$52.38	$52.40	$52.40
Purchase #3	$13.63	9.837%	$14.9708	$14.97	$14.95	$15.00
Purchase #4	$172.66	4.255%	$180.0067	$180.01	$180.00	$180.00
Purchase #5	$50.59	3.279%	$52.2488	$52.25	$52.25	$52.20
Purchase #6	$167.59	4.724%	$175.507	$175.51	$175.50	$175.50
Purchase #7	$85.73	10.786%	$94.9768	$94.98	$95.00	$95.00
7 purchase totals =	$601.38		$641.8774	$641.88	$641.90	$641.90