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	$128.48	11.828%	$143.6766	$143.68	$143.70	$143.70
Purchase #2	$135.93	7.382%	$145.9644	$145.96	$145.95	$146.00
Purchase #3	$190.29	13.191%	$215.3912	$215.39	$215.40	$215.40
Purchase #4	$81.56	9.722%	$89.4893	$89.49	$89.50	$89.50
Purchase #5	$167.59	6.531%	$178.5353	$178.54	$178.55	$178.50
Purchase #6	$246.29	11.465%	$274.5271	$274.53	$274.55	$274.50
Purchase #7	$171.78	12.136%	$192.6272	$192.63	$192.65	$192.60
7 purchase totals =	$1,121.92		$1,240.2111	$1,240.22	$1,240.30	$1,240.20