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	$37.81	11.235%	$42.058	$42.06	$42.05	$42.10
Purchase #2	$86.47	3.289%	$89.314	$89.31	$89.30	$89.30
Purchase #3	$112.87	9.798%	$123.929	$123.93	$123.95	$123.90
Purchase #4	$64.73	12.759%	$72.9889	$72.99	$73.00	$73.00
Purchase #5	$93.74	8.362%	$101.5785	$101.58	$101.60	$101.60
Purchase #6	$213.42	8.408%	$231.3644	$231.36	$231.35	$231.40
Purchase #7	$109.44	5.258%	$115.1944	$115.19	$115.20	$115.20
7 purchase totals =	$718.48		$776.4272	$776.42	$776.45	$776.50