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	$242.25	5.724%	$256.1164	$256.12	$256.10	$256.10
Purchase #2	$76.37	5.490%	$80.5627	$80.56	$80.55	$80.60
Purchase #3	$178.66	10.187%	$196.8601	$196.86	$196.85	$196.90
Purchase #4	$63.97	12.328%	$71.8562	$71.86	$71.85	$71.90
Purchase #5	$104.27	4.329%	$108.7838	$108.78	$108.80	$108.80
Purchase #6	$83.88	5.690%	$88.6528	$88.65	$88.65	$88.70
Purchase #7	$213.32	3.470%	$220.7222	$220.72	$220.70	$220.70
7 purchase totals =	$962.72		$1,023.5542	$1,023.55	$1,023.50	$1,023.70