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	$6.61	11.106%	$7.3441	$7.34	$7.35	$7.30
Purchase #2	$226.56	9.195%	$247.3922	$247.39	$247.40	$247.40
Purchase #3	$111.33	5.285%	$117.2138	$117.21	$117.20	$117.20
Purchase #4	$187.45	4.776%	$196.4026	$196.40	$196.40	$196.40
Purchase #5	$43.60	6.153%	$46.2827	$46.28	$46.30	$46.30
Purchase #6	$166.41	8.684%	$180.861	$180.86	$180.85	$180.90
Purchase #7	$62.43	5.366%	$65.78	$65.78	$65.80	$65.80
7 purchase totals =	$804.39		$861.2764	$861.26	$861.30	$861.30