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	$17.48	6.360%	$18.5917	$18.59	$18.60	$18.60
Purchase #2	$40.97	6.719%	$43.7228	$43.72	$43.70	$43.70
Purchase #3	$31.29	7.733%	$33.7097	$33.71	$33.70	$33.70
Purchase #4	$234.99	4.609%	$245.8207	$245.82	$245.80	$245.80
Purchase #5	$100.77	11.110%	$111.9655	$111.97	$111.95	$112.00
Purchase #6	$62.73	3.798%	$65.1125	$65.11	$65.10	$65.10
Purchase #7	$160.90	6.324%	$171.0753	$171.08	$171.10	$171.10
7 purchase totals =	$649.13		$689.9982	$690.00	$689.95	$690.00