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	$155.90	6.447%	$165.9509	$165.95	$165.95	$166.00
Purchase #2	$12.40	8.499%	$13.4539	$13.45	$13.45	$13.50
Purchase #3	$100.78	10.154%	$111.0132	$111.01	$111.00	$111.00
Purchase #4	$188.42	6.116%	$199.9438	$199.94	$199.95	$199.90
Purchase #5	$140.97	12.668%	$158.8281	$158.83	$158.85	$158.80
Purchase #6	$104.60	11.406%	$116.5307	$116.53	$116.55	$116.50
Purchase #7	$246.85	3.775%	$256.1686	$256.17	$256.15	$256.20
7 purchase totals =	$949.92		$1,021.8892	$1,021.88	$1,021.90	$1,021.90