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	$187.41	10.409%	$206.9175	$206.92	$206.90	$206.90
Purchase #2	$105.93	3.183%	$109.3018	$109.30	$109.30	$109.30
Purchase #3	$168.79	6.250%	$179.3394	$179.34	$179.35	$179.30
Purchase #4	$226.94	13.183%	$256.8575	$256.86	$256.85	$256.90
Purchase #5	$228.70	8.189%	$247.4282	$247.43	$247.45	$247.40
Purchase #6	$143.28	12.298%	$160.9006	$160.90	$160.90	$160.90
Purchase #7	$240.86	3.728%	$249.8393	$249.84	$249.85	$249.80
7 purchase totals =	$1,301.91		$1,410.5843	$1,410.59	$1,410.60	$1,410.50