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	$216.47	12.839%	$244.2626	$244.26	$244.25	$244.30
Purchase #2	$94.55	9.280%	$103.3242	$103.32	$103.30	$103.30
Purchase #3	$56.25	5.196%	$59.1728	$59.17	$59.15	$59.20
Purchase #4	$184.34	10.149%	$203.0487	$203.05	$203.05	$203.00
Purchase #5	$238.90	6.339%	$254.0439	$254.04	$254.05	$254.00
Purchase #6	$28.95	9.579%	$31.7231	$31.72	$31.70	$31.70
Purchase #7	$138.56	4.354%	$144.5929	$144.59	$144.60	$144.60
7 purchase totals =	$958.02		$1,040.1682	$1,040.15	$1,040.10	$1,040.10