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	$64.62	12.314%	$72.5773	$72.58	$72.60	$72.60
Purchase #2	$65.78	10.688%	$72.8106	$72.81	$72.80	$72.80
Purchase #3	$151.32	5.393%	$159.4807	$159.48	$159.50	$159.50
Purchase #4	$159.75	12.672%	$179.9935	$179.99	$180.00	$180.00
Purchase #5	$131.69	6.548%	$140.3131	$140.31	$140.30	$140.30
Purchase #6	$94.94	6.753%	$101.3513	$101.35	$101.35	$101.40
Purchase #7	$116.66	8.501%	$126.5773	$126.58	$126.60	$126.60
7 purchase totals =	$784.76		$853.1038	$853.10	$853.15	$853.20