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	$153.79	9.168%	$167.8895	$167.89	$167.90	$167.90
Purchase #2	$180.74	5.314%	$190.3445	$190.34	$190.35	$190.30
Purchase #3	$154.59	7.541%	$166.2476	$166.25	$166.25	$166.20
Purchase #4	$38.64	3.779%	$40.1002	$40.10	$40.10	$40.10
Purchase #5	$88.88	12.868%	$100.3171	$100.32	$100.30	$100.30
Purchase #6	$168.32	5.798%	$178.0792	$178.08	$178.10	$178.10
Purchase #7	$144.80	5.665%	$153.0029	$153.00	$153.00	$153.00
7 purchase totals =	$929.76		$995.9810	$995.98	$996.00	$995.90