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	$154.83	13.140%	$175.1747	$175.17	$175.15	$175.20
Purchase #2	$15.54	9.785%	$17.0606	$17.06	$17.05	$17.10
Purchase #3	$155.30	6.183%	$164.9022	$164.90	$164.90	$164.90
Purchase #4	$248.31	13.135%	$280.9255	$280.93	$280.95	$280.90
Purchase #5	$44.38	9.761%	$48.7119	$48.71	$48.70	$48.70
Purchase #6	$77.73	10.479%	$85.8753	$85.88	$85.90	$85.90
Purchase #7	$97.73	6.872%	$104.446	$104.45	$104.45	$104.40
7 purchase totals =	$793.82		$877.0962	$877.10	$877.10	$877.10