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	$246.59	3.183%	$254.439	$254.44	$254.45	$254.40
Purchase #2	$188.90	7.515%	$203.0958	$203.10	$203.10	$203.10
Purchase #3	$76.80	11.614%	$85.7196	$85.72	$85.70	$85.70
Purchase #4	$38.70	9.589%	$42.4109	$42.41	$42.40	$42.40
Purchase #5	$88.78	12.579%	$99.9476	$99.95	$99.95	$99.90
Purchase #6	$176.52	3.591%	$182.8588	$182.86	$182.85	$182.90
Purchase #7	$154.61	12.290%	$173.6116	$173.61	$173.60	$173.60
7 purchase totals =	$970.90		$1,042.0833	$1,042.09	$1,042.05	$1,042.00