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	$39.36	7.412%	$42.2774	$42.28	$42.30	$42.30
Purchase #2	$99.68	3.565%	$103.2336	$103.23	$103.25	$103.20
Purchase #3	$89.40	8.665%	$97.1465	$97.15	$97.15	$97.10
Purchase #4	$104.47	10.642%	$115.5877	$115.59	$115.60	$115.60
Purchase #5	$48.94	10.711%	$54.182	$54.18	$54.20	$54.20
Purchase #6	$114.81	12.689%	$129.3782	$129.38	$129.40	$129.40
Purchase #7	$38.78	3.702%	$40.2156	$40.22	$40.20	$40.20
7 purchase totals =	$535.44		$582.0210	$582.03	$582.10	$582.00