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	$163.25	13.269%	$184.9116	$184.91	$184.90	$184.90
Purchase #2	$31.55	7.778%	$34.004	$34.00	$34.00	$34.00
Purchase #3	$201.85	4.113%	$210.1521	$210.15	$210.15	$210.20
Purchase #4	$36.38	6.704%	$38.8189	$38.82	$38.80	$38.80
Purchase #5	$25.69	8.167%	$27.7881	$27.79	$27.80	$27.80
Purchase #6	$34.78	6.494%	$37.0386	$37.04	$37.05	$37.00
Purchase #7	$179.29	9.807%	$196.873	$196.87	$196.85	$196.90
7 purchase totals =	$672.79		$729.5863	$729.58	$729.55	$729.60