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	$103.66	6.308%	$110.1989	$110.20	$110.20	$110.20
Purchase #2	$135.41	3.348%	$139.9435	$139.94	$139.95	$139.90
Purchase #3	$37.94	10.506%	$41.926	$41.93	$41.95	$41.90
Purchase #4	$224.41	4.243%	$233.9317	$233.93	$233.95	$233.90
Purchase #5	$78.95	9.530%	$86.4739	$86.47	$86.45	$86.50
Purchase #6	$220.88	13.174%	$249.9787	$249.98	$250.00	$250.00
Purchase #7	$112.57	13.663%	$127.9504	$127.95	$127.95	$128.00
7 purchase totals =	$913.82		$990.4031	$990.40	$990.45	$990.40