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	$145.79	3.328%	$150.6419	$150.64	$150.65	$150.60
Purchase #2	$109.65	12.411%	$123.2587	$123.26	$123.25	$123.30
Purchase #3	$105.44	9.802%	$115.7752	$115.78	$115.80	$115.80
Purchase #4	$184.38	4.563%	$192.7933	$192.79	$192.80	$192.80
Purchase #5	$86.53	3.358%	$89.4357	$89.44	$89.45	$89.40
Purchase #6	$103.67	11.379%	$115.4666	$115.47	$115.45	$115.50
Purchase #7	$83.52	3.275%	$86.2553	$86.26	$86.25	$86.30
7 purchase totals =	$818.98		$873.6267	$873.64	$873.65	$873.70