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	$13.28	11.712%	$14.8354	$14.84	$14.85	$14.80
Purchase #2	$215.41	6.583%	$229.5904	$229.59	$229.60	$229.60
Purchase #3	$20.28	3.586%	$21.0072	$21.01	$21.00	$21.00
Purchase #4	$242.98	5.438%	$256.1933	$256.19	$256.20	$256.20
Purchase #5	$239.55	6.317%	$254.6824	$254.68	$254.70	$254.70
Purchase #6	$83.28	9.606%	$91.2799	$91.28	$91.30	$91.30
Purchase #7	$127.39	7.430%	$136.8551	$136.86	$136.85	$136.90
7 purchase totals =	$942.17		$1,004.4437	$1,004.45	$1,004.50	$1,004.50