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	$53.89	6.690%	$57.4952	$57.50	$57.50	$57.50
Purchase #2	$116.87	5.843%	$123.6987	$123.70	$123.70	$123.70
Purchase #3	$31.30	9.730%	$34.3455	$34.35	$34.35	$34.30
Purchase #4	$63.85	12.546%	$71.8606	$71.86	$71.85	$71.90
Purchase #5	$55.94	5.483%	$59.0072	$59.01	$59.00	$59.00
Purchase #6	$224.47	5.683%	$237.2266	$237.23	$237.25	$237.20
Purchase #7	$186.58	7.332%	$200.26	$200.26	$200.25	$200.30
7 purchase totals =	$732.90		$783.8938	$783.91	$783.90	$783.90