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	$65.44	12.158%	$73.3962	$73.40	$73.40	$73.40
Purchase #2	$28.46	12.596%	$32.0448	$32.04	$32.05	$32.00
Purchase #3	$132.83	13.373%	$150.5934	$150.59	$150.60	$150.60
Purchase #4	$160.79	10.752%	$178.0781	$178.08	$178.10	$178.10
Purchase #5	$239.48	7.785%	$258.1235	$258.12	$258.10	$258.10
Purchase #6	$247.41	4.320%	$258.0981	$258.10	$258.10	$258.10
Purchase #7	$197.81	11.860%	$221.2703	$221.27	$221.25	$221.30
7 purchase totals =	$1,072.22		$1,171.6044	$1,171.60	$1,171.60	$1,171.60