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	$139.46	10.631%	$154.286	$154.29	$154.30	$154.30
Purchase #2	$191.55	3.353%	$197.9727	$197.97	$197.95	$198.00
Purchase #3	$148.84	13.863%	$169.4737	$169.47	$169.45	$169.50
Purchase #4	$73.88	11.354%	$82.2683	$82.27	$82.25	$82.30
Purchase #5	$35.59	12.296%	$39.9661	$39.97	$39.95	$40.00
Purchase #6	$99.83	3.256%	$103.0805	$103.08	$103.10	$103.10
Purchase #7	$164.96	12.406%	$185.4249	$185.42	$185.40	$185.40
7 purchase totals =	$854.11		$932.4722	$932.47	$932.40	$932.60