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	$97.62	10.179%	$107.5567	$107.56	$107.55	$107.60
Purchase #2	$180.60	8.693%	$196.2996	$196.30	$196.30	$196.30
Purchase #3	$87.34	9.806%	$95.9046	$95.90	$95.90	$95.90
Purchase #4	$168.94	6.715%	$180.2843	$180.28	$180.30	$180.30
Purchase #5	$242.28	11.339%	$269.7521	$269.75	$269.75	$269.80
Purchase #6	$33.67	4.813%	$35.2905	$35.29	$35.30	$35.30
Purchase #7	$99.78	9.329%	$109.0885	$109.09	$109.10	$109.10
7 purchase totals =	$910.23		$994.1763	$994.17	$994.20	$994.30