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	$159.68	11.858%	$178.6149	$178.61	$178.60	$178.60
Purchase #2	$41.65	4.413%	$43.488	$43.49	$43.50	$43.50
Purchase #3	$31.37	6.681%	$33.4658	$33.47	$33.45	$33.50
Purchase #4	$125.59	3.187%	$129.5926	$129.59	$129.60	$129.60
Purchase #5	$10.46	6.321%	$11.1212	$11.12	$11.10	$11.10
Purchase #6	$98.92	4.555%	$103.4258	$103.43	$103.45	$103.40
Purchase #7	$28.42	8.764%	$30.9107	$30.91	$30.90	$30.90
7 purchase totals =	$496.09		$530.6190	$530.62	$530.60	$530.60