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	$210.60	5.501%	$222.1851	$222.19	$222.20	$222.20
Purchase #2	$213.73	9.849%	$234.7803	$234.78	$234.80	$234.80
Purchase #3	$249.66	7.308%	$267.9052	$267.91	$267.90	$267.90
Purchase #4	$149.51	6.278%	$158.8962	$158.90	$158.90	$158.90
Purchase #5	$115.76	9.710%	$127.0003	$127.00	$127.00	$127.00
Purchase #6	$59.50	4.649%	$62.2662	$62.27	$62.25	$62.30
Purchase #7	$132.60	9.460%	$145.144	$145.14	$145.15	$145.10
7 purchase totals =	$1,131.36		$1,218.1773	$1,218.19	$1,218.20	$1,218.20