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	$139.34	13.669%	$158.3864	$158.39	$158.40	$158.40
Purchase #2	$99.90	13.336%	$113.2227	$113.22	$113.20	$113.20
Purchase #3	$12.93	7.516%	$13.9018	$13.90	$13.90	$13.90
Purchase #4	$187.62	4.477%	$196.0197	$196.02	$196.00	$196.00
Purchase #5	$134.46	3.249%	$138.8286	$138.83	$138.85	$138.80
Purchase #6	$122.52	3.675%	$127.0226	$127.02	$127.00	$127.00
Purchase #7	$186.44	13.645%	$211.8797	$211.88	$211.90	$211.90
7 purchase totals =	$883.21		$959.2615	$959.26	$959.25	$959.20