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	$39.74	11.447%	$44.289	$44.29	$44.30	$44.30
Purchase #2	$102.94	8.135%	$111.3142	$111.31	$111.30	$111.30
Purchase #3	$89.58	10.433%	$98.9259	$98.93	$98.95	$98.90
Purchase #4	$128.78	11.303%	$143.336	$143.34	$143.35	$143.30
Purchase #5	$229.32	7.724%	$247.0327	$247.03	$247.05	$247.00
Purchase #6	$224.76	13.162%	$254.3429	$254.34	$254.35	$254.30
Purchase #7	$95.96	3.729%	$99.5383	$99.54	$99.55	$99.50
7 purchase totals =	$911.08		$998.7790	$998.78	$998.85	$998.60