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	$57.29	4.374%	$59.7959	$59.80	$59.80	$59.80
Purchase #2	$207.86	12.356%	$233.5432	$233.54	$233.55	$233.50
Purchase #3	$121.30	5.844%	$128.3888	$128.39	$128.40	$128.40
Purchase #4	$40.41	12.227%	$45.3509	$45.35	$45.35	$45.40
Purchase #5	$38.99	11.239%	$43.3721	$43.37	$43.35	$43.40
Purchase #6	$88.69	6.423%	$94.3866	$94.39	$94.40	$94.40
Purchase #7	$124.53	6.478%	$132.5971	$132.60	$132.60	$132.60
7 purchase totals =	$679.07		$737.4346	$737.44	$737.45	$737.50