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	$90.65	9.768%	$99.5047	$99.50	$99.50	$99.50
Purchase #2	$158.96	8.426%	$172.354	$172.35	$172.35	$172.40
Purchase #3	$181.47	9.511%	$198.7296	$198.73	$198.75	$198.70
Purchase #4	$99.97	6.808%	$106.776	$106.78	$106.80	$106.80
Purchase #5	$33.51	7.227%	$35.9318	$35.93	$35.95	$35.90
Purchase #6	$148.55	13.296%	$168.3012	$168.30	$168.30	$168.30
Purchase #7	$206.73	9.826%	$227.0433	$227.04	$227.05	$227.00
7 purchase totals =	$919.84		$1,008.6406	$1,008.63	$1,008.70	$1,008.60