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	$38.72	9.856%	$42.5362	$42.54	$42.55	$42.50
Purchase #2	$169.81	3.862%	$176.3681	$176.37	$176.35	$176.40
Purchase #3	$215.56	9.673%	$236.4111	$236.41	$236.40	$236.40
Purchase #4	$82.51	9.580%	$90.4145	$90.41	$90.40	$90.40
Purchase #5	$42.56	3.421%	$44.016	$44.02	$44.00	$44.00
Purchase #6	$142.34	8.409%	$154.3094	$154.31	$154.30	$154.30
Purchase #7	$204.30	10.472%	$225.6943	$225.69	$225.70	$225.70
7 purchase totals =	$895.80		$969.7496	$969.75	$969.70	$969.70