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	$80.37	12.382%	$90.3214	$90.32	$90.30	$90.30
Purchase #2	$117.63	10.523%	$130.0082	$130.01	$130.00	$130.00
Purchase #3	$35.88	13.150%	$40.5982	$40.60	$40.60	$40.60
Purchase #4	$38.97	12.357%	$43.7855	$43.79	$43.80	$43.80
Purchase #5	$88.55	10.517%	$97.8628	$97.86	$97.85	$97.90
Purchase #6	$54.44	10.462%	$60.1355	$60.14	$60.15	$60.10
Purchase #7	$221.83	4.106%	$230.9383	$230.94	$230.95	$230.90
7 purchase totals =	$637.67		$693.6499	$693.66	$693.65	$693.60