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	$132.59	4.463%	$138.5075	$138.51	$138.50	$138.50
Purchase #2	$223.85	8.158%	$242.1117	$242.11	$242.10	$242.10
Purchase #3	$94.38	7.558%	$101.5132	$101.51	$101.50	$101.50
Purchase #4	$59.78	9.314%	$65.3479	$65.35	$65.35	$65.30
Purchase #5	$118.92	3.494%	$123.0751	$123.08	$123.10	$123.10
Purchase #6	$222.40	4.546%	$232.5103	$232.51	$232.50	$232.50
Purchase #7	$26.60	10.636%	$29.4292	$29.43	$29.45	$29.40
7 purchase totals =	$878.52		$932.4949	$932.50	$932.50	$932.40