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	$238.37	11.818%	$266.5406	$266.54	$266.55	$266.50
Purchase #2	$129.71	9.667%	$142.2491	$142.25	$142.25	$142.20
Purchase #3	$6.71	7.855%	$7.2371	$7.24	$7.25	$7.20
Purchase #4	$40.78	3.379%	$42.158	$42.16	$42.15	$42.20
Purchase #5	$146.94	10.589%	$162.4995	$162.50	$162.50	$162.50
Purchase #6	$116.27	6.646%	$123.9973	$124.00	$124.00	$124.00
Purchase #7	$90.75	8.308%	$98.2895	$98.29	$98.30	$98.30
7 purchase totals =	$769.53		$842.9711	$842.98	$843.00	$842.90