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	$123.82	3.839%	$128.5734	$128.57	$128.55	$128.60
Purchase #2	$75.86	3.495%	$78.5113	$78.51	$78.50	$78.50
Purchase #3	$205.54	13.348%	$232.9755	$232.98	$233.00	$233.00
Purchase #4	$221.64	6.602%	$236.2727	$236.27	$236.25	$236.30
Purchase #5	$228.94	6.215%	$243.1686	$243.17	$243.15	$243.20
Purchase #6	$110.61	7.258%	$118.6381	$118.64	$118.65	$118.60
Purchase #7	$131.35	12.866%	$148.2495	$148.25	$148.25	$148.20
7 purchase totals =	$1,097.76		$1,186.3891	$1,186.39	$1,186.35	$1,186.40