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	$249.58	12.355%	$280.4156	$280.42	$280.40	$280.40
Purchase #2	$59.39	9.541%	$65.0564	$65.06	$65.05	$65.10
Purchase #3	$127.83	12.194%	$143.4176	$143.42	$143.40	$143.40
Purchase #4	$75.58	4.449%	$78.9426	$78.94	$78.95	$78.90
Purchase #5	$153.57	4.663%	$160.731	$160.73	$160.75	$160.70
Purchase #6	$106.83	11.605%	$119.2276	$119.23	$119.25	$119.20
Purchase #7	$222.57	4.519%	$232.6279	$232.63	$232.65	$232.60
7 purchase totals =	$995.35		$1,080.4187	$1,080.43	$1,080.45	$1,080.30