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	$18.50	9.643%	$20.284	$20.28	$20.30	$20.30
Purchase #2	$182.37	12.673%	$205.4818	$205.48	$205.50	$205.50
Purchase #3	$235.61	12.346%	$264.6984	$264.70	$264.70	$264.70
Purchase #4	$211.32	7.438%	$227.038	$227.04	$227.05	$227.00
Purchase #5	$109.77	12.124%	$123.0785	$123.08	$123.10	$123.10
Purchase #6	$142.66	12.574%	$160.5981	$160.60	$160.60	$160.60
Purchase #7	$38.29	13.697%	$43.5346	$43.53	$43.55	$43.50
7 purchase totals =	$938.52		$1,044.7134	$1,044.71	$1,044.80	$1,044.70