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	$35.30	6.433%	$37.5708	$37.57	$37.55	$37.60
Purchase #2	$190.57	3.293%	$196.8455	$196.85	$196.85	$196.80
Purchase #3	$118.62	7.874%	$127.9601	$127.96	$127.95	$128.00
Purchase #4	$62.86	6.723%	$67.0861	$67.09	$67.10	$67.10
Purchase #5	$102.71	3.379%	$106.1806	$106.18	$106.20	$106.20
Purchase #6	$189.50	12.242%	$212.6986	$212.70	$212.70	$212.70
Purchase #7	$175.78	5.214%	$184.9452	$184.95	$184.95	$184.90
7 purchase totals =	$875.34		$933.2869	$933.30	$933.30	$933.30