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	$159.51	11.627%	$178.0562	$178.06	$178.05	$178.10
Purchase #2	$38.81	3.760%	$40.2693	$40.27	$40.25	$40.30
Purchase #3	$94.92	9.409%	$103.851	$103.85	$103.85	$103.90
Purchase #4	$176.87	4.538%	$184.8964	$184.90	$184.90	$184.90
Purchase #5	$225.95	11.521%	$251.9817	$251.98	$252.00	$252.00
Purchase #6	$200.94	12.368%	$225.7923	$225.79	$225.80	$225.80
Purchase #7	$58.90	10.786%	$65.253	$65.25	$65.25	$65.30
7 purchase totals =	$955.90		$1,050.0999	$1,050.10	$1,050.10	$1,050.30