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	$43.89	6.779%	$46.8653	$46.87	$46.85	$46.90
Purchase #2	$179.90	10.351%	$198.5214	$198.52	$198.50	$198.50
Purchase #3	$32.81	6.782%	$35.0352	$35.04	$35.05	$35.00
Purchase #4	$117.25	6.668%	$125.0682	$125.07	$125.05	$125.10
Purchase #5	$80.29	11.447%	$89.4808	$89.48	$89.50	$89.50
Purchase #6	$107.82	9.869%	$118.4608	$118.46	$118.45	$118.50
Purchase #7	$47.37	5.321%	$49.8906	$49.89	$49.90	$49.90
7 purchase totals =	$609.33		$663.3223	$663.33	$663.30	$663.40