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	$85.31	6.481%	$90.8389	$90.84	$90.85	$90.80
Purchase #2	$38.32	11.484%	$42.7207	$42.72	$42.70	$42.70
Purchase #3	$112.55	5.256%	$118.4656	$118.47	$118.45	$118.50
Purchase #4	$221.41	8.500%	$240.2299	$240.23	$240.25	$240.20
Purchase #5	$141.88	9.738%	$155.6963	$155.70	$155.70	$155.70
Purchase #6	$239.51	7.487%	$257.4421	$257.44	$257.45	$257.40
Purchase #7	$189.51	11.551%	$211.4003	$211.40	$211.40	$211.40
7 purchase totals =	$1,028.49		$1,116.7938	$1,116.80	$1,116.80	$1,116.70