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	$178.59	4.643%	$186.8819	$186.88	$186.90	$186.90
Purchase #2	$20.37	13.459%	$23.1116	$23.11	$23.10	$23.10
Purchase #3	$44.57	5.705%	$47.1127	$47.11	$47.10	$47.10
Purchase #4	$38.34	11.842%	$42.8802	$42.88	$42.90	$42.90
Purchase #5	$201.32	8.724%	$218.8832	$218.88	$218.90	$218.90
Purchase #6	$245.61	7.278%	$263.4855	$263.49	$263.50	$263.50
Purchase #7	$80.90	12.297%	$90.8483	$90.85	$90.85	$90.80
7 purchase totals =	$809.70		$873.2034	$873.20	$873.25	$873.20