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	$52.33	7.248%	$56.1229	$56.12	$56.10	$56.10
Purchase #2	$109.61	9.177%	$119.6689	$119.67	$119.65	$119.70
Purchase #3	$126.25	12.804%	$142.4151	$142.42	$142.40	$142.40
Purchase #4	$100.55	4.759%	$105.3352	$105.34	$105.35	$105.30
Purchase #5	$235.32	11.675%	$262.7936	$262.79	$262.80	$262.80
Purchase #6	$132.65	6.581%	$141.3797	$141.38	$141.40	$141.40
Purchase #7	$12.83	11.668%	$14.327	$14.33	$14.35	$14.30
7 purchase totals =	$769.54		$842.0424	$842.05	$842.05	$842.00