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	$100.76	10.685%	$111.5262	$111.53	$111.55	$111.50
Purchase #2	$161.52	6.353%	$171.7814	$171.78	$171.80	$171.80
Purchase #3	$183.57	12.245%	$206.0481	$206.05	$206.05	$206.00
Purchase #4	$116.59	11.150%	$129.5898	$129.59	$129.60	$129.60
Purchase #5	$63.88	13.393%	$72.4354	$72.44	$72.45	$72.40
Purchase #6	$101.95	7.641%	$109.74	$109.74	$109.75	$109.70
Purchase #7	$49.77	5.337%	$52.4262	$52.43	$52.45	$52.40
7 purchase totals =	$778.04		$853.5471	$853.56	$853.65	$853.40