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	$170.64	5.811%	$180.5559	$180.56	$180.55	$180.60
Purchase #2	$166.80	4.455%	$174.2309	$174.23	$174.25	$174.20
Purchase #3	$91.88	11.657%	$102.5905	$102.59	$102.60	$102.60
Purchase #4	$84.71	6.704%	$90.389	$90.39	$90.40	$90.40
Purchase #5	$59.74	3.408%	$61.7759	$61.78	$61.80	$61.80
Purchase #6	$131.94	7.866%	$142.3184	$142.32	$142.30	$142.30
Purchase #7	$144.39	13.487%	$163.8639	$163.86	$163.85	$163.90
7 purchase totals =	$850.10		$915.7245	$915.73	$915.75	$915.80