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	$117.53	12.143%	$131.8017	$131.80	$131.80	$131.80
Purchase #2	$38.42	10.144%	$42.3173	$42.32	$42.30	$42.30
Purchase #3	$52.89	6.642%	$56.403	$56.40	$56.40	$56.40
Purchase #4	$192.81	10.841%	$213.7125	$213.71	$213.70	$213.70
Purchase #5	$118.36	4.665%	$123.8815	$123.88	$123.90	$123.90
Purchase #6	$185.51	6.395%	$197.3734	$197.37	$197.35	$197.40
Purchase #7	$74.98	9.127%	$81.8234	$81.82	$81.80	$81.80
7 purchase totals =	$780.50		$847.3128	$847.30	$847.25	$847.30