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	$153.56	4.392%	$160.3044	$160.30	$160.30	$160.30
Purchase #2	$127.50	12.520%	$143.463	$143.46	$143.45	$143.50
Purchase #3	$185.60	8.277%	$200.9621	$200.96	$200.95	$201.00
Purchase #4	$245.81	7.480%	$264.1966	$264.20	$264.20	$264.20
Purchase #5	$173.70	8.265%	$188.0563	$188.06	$188.05	$188.10
Purchase #6	$27.66	9.551%	$30.3018	$30.30	$30.30	$30.30
Purchase #7	$132.73	5.754%	$140.3673	$140.37	$140.35	$140.40
7 purchase totals =	$1,046.56		$1,127.6515	$1,127.65	$1,127.60	$1,127.80