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	$80.37	11.636%	$89.7219	$89.72	$89.70	$89.70
Purchase #2	$49.35	11.629%	$55.0889	$55.09	$55.10	$55.10
Purchase #3	$63.70	13.798%	$72.4893	$72.49	$72.50	$72.50
Purchase #4	$142.36	3.139%	$146.8287	$146.83	$146.85	$146.80
Purchase #5	$178.73	5.803%	$189.1017	$189.10	$189.10	$189.10
Purchase #6	$27.78	11.625%	$31.0094	$31.01	$31.00	$31.00
Purchase #7	$28.32	9.483%	$31.0056	$31.01	$31.00	$31.00
7 purchase totals =	$570.61		$615.2455	$615.25	$615.25	$615.20