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	$88.64	13.458%	$100.5692	$100.57	$100.55	$100.60
Purchase #2	$40.48	12.578%	$45.5716	$45.57	$45.55	$45.60
Purchase #3	$72.57	11.314%	$80.7806	$80.78	$80.80	$80.80
Purchase #4	$122.90	7.329%	$131.9073	$131.91	$131.90	$131.90
Purchase #5	$112.65	12.417%	$126.6378	$126.64	$126.65	$126.60
Purchase #6	$217.38	13.626%	$247.0002	$247.00	$247.00	$247.00
Purchase #7	$110.47	5.643%	$116.7038	$116.70	$116.70	$116.70
7 purchase totals =	$765.09		$849.1705	$849.17	$849.15	$849.20