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	$101.79	9.560%	$111.5211	$111.52	$111.50	$111.50
Purchase #2	$139.61	12.798%	$157.4773	$157.48	$157.50	$157.50
Purchase #3	$120.32	3.646%	$124.7069	$124.71	$124.70	$124.70
Purchase #4	$47.73	7.632%	$51.3728	$51.37	$51.35	$51.40
Purchase #5	$73.51	3.511%	$76.0909	$76.09	$76.10	$76.10
Purchase #6	$178.76	6.311%	$190.0415	$190.04	$190.05	$190.00
Purchase #7	$64.49	10.255%	$71.1034	$71.10	$71.10	$71.10
7 purchase totals =	$726.21		$782.3139	$782.31	$782.30	$782.30