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	$49.32	13.559%	$56.0073	$56.01	$56.00	$56.00
Purchase #2	$102.56	13.345%	$116.2466	$116.25	$116.25	$116.20
Purchase #3	$23.95	6.293%	$25.4572	$25.46	$25.45	$25.50
Purchase #4	$141.33	7.459%	$151.8718	$151.87	$151.85	$151.90
Purchase #5	$60.47	5.309%	$63.6804	$63.68	$63.70	$63.70
Purchase #6	$202.29	4.720%	$211.8381	$211.84	$211.85	$211.80
Purchase #7	$40.68	3.255%	$42.0041	$42.00	$42.00	$42.00
7 purchase totals =	$620.60		$667.1055	$667.11	$667.10	$667.10