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	$48.49	9.118%	$52.9113	$52.91	$52.90	$52.90
Purchase #2	$140.45	10.402%	$155.0596	$155.06	$155.05	$155.10
Purchase #3	$85.72	9.566%	$93.92	$93.92	$93.90	$93.90
Purchase #4	$112.34	3.713%	$116.5112	$116.51	$116.50	$116.50
Purchase #5	$17.88	3.255%	$18.462	$18.46	$18.45	$18.50
Purchase #6	$169.79	8.568%	$184.3376	$184.34	$184.35	$184.30
Purchase #7	$109.68	12.859%	$123.7838	$123.78	$123.80	$123.80
7 purchase totals =	$684.35		$744.9855	$744.98	$744.95	$745.00