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	$111.88	10.154%	$123.2403	$123.24	$123.25	$123.20
Purchase #2	$118.92	6.379%	$126.5059	$126.51	$126.50	$126.50
Purchase #3	$243.87	3.234%	$251.7568	$251.76	$251.75	$251.80
Purchase #4	$186.32	9.700%	$204.393	$204.39	$204.40	$204.40
Purchase #5	$52.88	9.725%	$58.0226	$58.02	$58.00	$58.00
Purchase #6	$92.88	11.481%	$103.5436	$103.54	$103.55	$103.50
Purchase #7	$152.59	12.704%	$171.975	$171.98	$172.00	$172.00
7 purchase totals =	$959.34		$1,039.4372	$1,039.44	$1,039.45	$1,039.40